annotate ProteinDigestor.pl @ 0:163892325845 draft default tip

Initial commit.

#!/usr/bin/perl -w

###############################################################
# ProteinDigestor.pl
# 
# =====================================================
# $Id: ProteinDigestor.pl 76 2011-01-04 13:16:56Z [e-mail] $
# $URL: https://trac.nbic.nl/svn/galaxytools/trunk/tools/general/FastaTools/ProteinDigestor.pl $
# $LastChangedDate: 2011-01-04 07:16:56 -0600 (Tue, 04 Jan 2011) $
# $LastChangedRevision: 76 $
# $LastChangedBy: [e-mail] $
# =====================================================
# 
# (c) Dr. Ir. B. van Breukelen et al.
# https://bioinformatics.chem.uu.nl
# http://www.netherlandsproteomicscentre.eu/ 
# [e-mail]
# 
# Software to create peptide databases from a fasta
# file of proteins. You can cut with several enzymes
# select on size, PI, etc etc etc.
#
# TODO: put filters, enzymes, in seperate config file
###############################################################

#############################
# Initialise environment
#############################
use strict;
use Getopt::Std;
use Log::Log4perl qw(:easy);

#
# Log levels for Log4perl.
#
my %log_levels = (
	'ALL'   => $ALL,
	'TRACE' => $TRACE,
	'DEBUG' => $DEBUG,
	'INFO'  => $INFO,
	'WARN'  => $WARN,
	'ERROR' => $ERROR,
	'FATAL' => $FATAL,
	'OFF'   => $OFF,
);

#
# pK values array
#
my %cPk = (
	'A'=>[3.55, 7.59, 0    , 0    , 0],
	'B'=>[3.55, 7.50, 0    , 0    , 0],
	'C'=>[3.55, 7.50, 9.00 , 9.00 , 9.00], 
	'D'=>[4.55, 7.50, 4.05 , 4.05 , 4.05],
	'E'=>[4.75, 7.70, 4.45 , 4.45 , 4.45],
	'F'=>[3.55, 7.50, 0    , 0.   , 0],
	'G'=>[3.55, 7.50, 0    , 0.   , 0],
	'H'=>[3.55, 7.50, 5.98 , 5.98 , 5.98],
 	'I'=>[3.55, 7.50, 0    , 0.   , 0.],
	'J'=>[0.00, 0.00, 0    , 0.   , 0.],
	'K'=>[3.55, 7.50, 10.00, 10.00, 10.00],
 	'L'=>[3.55, 7.50, 0    , 0.   , 0.],
 	'M'=>[3.55, 7.00, 0    , 0.   , 0.],
	'N'=>[3.55, 7.50, 0    , 0.   , 0.],
	'O'=>[0.00, 0.00, 0    , 0.   , 0.],
	'P'=>[3.55, 8.36, 0    , 0.   , 0.],
	'Q'=>[3.55, 7.50, 0    , 0.   , 0.],
	'R'=>[3.55, 7.50, 12.0 , 12.0 , 12.0],
	'S'=>[3.55, 6.93, 0    , 0.   , 0.],
	'T'=>[3.55, 6.82, 0    , 0.   , 0.],
	'U'=>[0.00, 0.00, 0    , 0.   , 0.],
	'V'=>[3.55, 7.44, 0    , 0.   , 0.],
	'W'=>[3.55, 7.50, 0    , 0.   , 0.],
	'X'=>[3.55, 7.50, 0    , 0.   , 0.],
	'Y'=>[3.55, 7.50, 10.00, 10.00, 10.00],
	'Z'=>[3.55, 7.50, 0    , 0.   , 0.]
);
		
#
# MW values array
#
my %cMWs = (
	'A'=>89.09,
	'B'=>132.65,
	'C'=>121.15,
	'D'=>133.1,
	'E'=>147.13,
	'F'=>165.19,
	'G'=>75.07,
	'H'=>155.16,
	'I'=>131.18,
	'J'=>0.00,
	'K'=>146.19,
	'L'=>131.18,
	'M'=>149.22,
	'N'=>132.12, 
	'O'=>0.00,
	'P'=>115.13,
	'Q'=>146.15,
	'R'=>174.21,
	'S'=>105.09,
	'T'=>119.12,
	'U'=>168.05,
	'V'=>117.15,
	'W'=>204.22,
	'X'=>129.26,
	'Y'=>181.19,
	'Z'=>146.73 
);

#  			
# Digestion enzymes.
#
# For example Trypsin cuts c-terminal of K and R not followed by a P at position p1 = c:K,R:P=1
#
my %enzymes = (
	'Trypsin'			=> 'c:K,R:P=1',
	'Trypsin/P'			=> 'c:K,R',
	'Chymotrypsin'		=> 'c:F,L,W,Y:P=1',
	'Chymotrypsin/P'	=> 'c:F,L,W,Y',
	'V8_E'				=> 'c:E,Z:P=1',
	'V8_DE'				=> 'c:E,D,B,Z:P=1',
	'LysC'				=> 'c:K:P=1',
	'LysC/P'			=> 'c:K',
	'LysN/P'			=> 'n:K'
);

my @filters = (
#	"[R|K][R|K][R|K]..[S|T]."
#	"[R|K][R|K][R|K].[S|T]." ,
#	"[R|K][R|K]..[S|T].",
#	"[R|K]..[S|T].",
#	"[R|K][R|K].[S|T].",
#	"[R|K].[S|T]."
#	"[S|T].[R|K]"
);
		
my %charges = ('A'=>0,	'B'=>0,	'C'=>0, 'D'=>-1, 'E'=>-1, 'F'=>0,'G'=>0, 'H'=>1, 'I'=>0,
				'J'=>0, 'K'=>1,	'L'=>0, 'M'=>0,	'N'=>0, 'O'=>0,'P'=>0, 'Q'=>0, 'R'=>1,
				'S'=>0, 'T'=>0,	'U'=>0, 'V'=>0,	'W'=>0, 'X'=>0,'Y'=>0, 'Z'=>0);
					
my %pept = ();	 #hashed array of peptides (HASH) and fasta headers (VALUE)		

my $H20 = 18.015; #Mol. weight water

my $PH_MIN = 0.0; #min pH value
my $PH_MAX = 14.0; #max pH value
my $MAXLOOP = 2000; # max number iterations
my $EPSI = 0.0001; # desired presision  			

#
# Get options.
#
my %opts;
Getopt::Std::getopts('i:o:e:r:p:m:n:c:l:sa', \%opts);

my $input						= $opts{'i'};
my $output						= $opts{'o'};
my $enzyme						= $opts{'e'};
my $enzyme_cleavage_site_rules	= $opts{'r'};
my $partial_cleavage			= $opts{'s'};
my $partial_cleavage_chance		= $opts{'p'};
my $min_peptide_weight			= $opts{'m'};
my $max_peptide_weight			= $opts{'n'};
my $max_charge					= $opts{'c'};
my $add_sequence_context		= $opts{'a'};
my $log_level					= $opts{'l'};

#
# Configure logging.
#
# Provides default if user did not specify log level:
$log_level = (defined($log_level) ? $log_level : 'INFO');

# Reset log level to default if user specified illegal log level.
$log_level = (
	defined($log_levels{$log_level})
	? $log_levels{$log_level}
	: $log_levels{'INFO'});

#Log::Log4perl->init('log4perl.properties');
Log::Log4perl->easy_init(

	#{ level    => $log_level,
	#  file     => ">>ProteinDigestor.log",
	#  layout   => '%F{1}-%L-%M: %m%n' },
	{
		level  => $log_level,
		file   => "STDOUT",
		layout => '%d L:%L %p> %m%n'
	},
);
my $logger = Log::Log4perl::get_logger();

#
# Check user input.
#
unless (defined($input) && defined($output)) {
	_Usage();
	exit;
}
if ($input =~ /^$/ || $output =~ /^$/) {
	_Usage();
	exit;
}
if ($input eq $output) {
	$logger->fatal('Output file is the same as the input file. Select a different file for the output.');
	exit;
}

#
# Check input file.
#
unless (-e $input && -f $input && -r $input) {
	$logger->fatal('Cannot read from input file ' . $input . ': ' . $!);
	exit;
}

#
# Set additional defaults.
#
$partial_cleavage			= (defined($partial_cleavage)			? $partial_cleavage			: 0);			# Disabled by default
$partial_cleavage_chance	= (defined($partial_cleavage_chance)	? $partial_cleavage_chance	: 0.1);			# 10% change by default
$add_sequence_context		= (defined($add_sequence_context)		? $add_sequence_context		: 0);			# Disabled by default

########################################################
# MAIN PROGRAM
########################################################

$logger->info('Starting...');

#
# Get protease cleavage site specs.
#
unless (defined($enzyme_cleavage_site_rules)) {
	
	#
	# Set default to Trypsin if the user did not specify an enzyme name nor a string with enzyme cleavage site rules.
	#
	$enzyme						= (defined($enzyme)						? $enzyme					: 'Trypsin');
	
	#
	# Check for illegal enzymes.
	#
	unless (defined($enzymes{$enzyme})) {
		$logger->fatal('Unkown enzyme ' . $enzyme . '.');
		exit;
	}
	
	#
	# Fetch enzyme cleavage site rules.
	#
	$enzyme_cleavage_site_rules = $enzymes{$enzyme};
	
}

$logger->info('Using enzyme cleavage site rules: ' . $enzyme_cleavage_site_rules);
my @split_params = split(/:/, $enzyme_cleavage_site_rules);
my $cut_term = $split_params[0];
my @cut_aa = split(/,/, $split_params[1]);
my @inhibition_aa;
if (defined($split_params[2])) {
	@inhibition_aa = split(/,/, $split_params[2]);
}
my $annotation = {};
my $sequence = '';

#
# Create filehandles.
#
open(my $input_fh,   "$input");
open(my $output_fh, ">$output");

#
# Write header to result file.
#
print($output_fh "Protein ID\tPeptide\tMW\tpI\tCharge\tnumber S\tnumber T\tnumber Y\n");

#
# Digest fasta files and store peptides in an array (hashed)
#
foreach my $line (<$input_fh>){
	
	if ($line =~ /^>/){
		
		#
		# We found a new FASTA header.
		#
		
		#
		# Process the previously found protein if we already found one.
		#
		unless ($sequence eq '') {
			_ProcessProtein();
		}
		
		#
		# Parse new FASTA header.
		#
		$line =~ s/[\r\n\f]+//g;
		$annotation = _ParseHeader($line);
		$sequence = '';
		
	} else {
		
		#
		# Found a sequence line.
		#
		$line =~ s/[\t\s\r\n\f0-9\*\-]+//g;
		$sequence .= $line;
	}
}

#
# Don't foget to process the last sequence!
#
_ProcessProtein();

close($input_fh);
close($output_fh);

$logger->info('Finished!');

#########################################################
# SUBS
#########################################################

sub _ProcessProtein {
	
	my $id = ${$annotation}{'ID'};
	$logger->debug('Accession/ID: ' . $id);
	$logger->debug('Sequence: ' . $sequence . "\n");
	my $total_length_sequence = length($sequence);
	my $total_peptide_length = 0;
	
	my ($peptides) = _Digest($sequence, $annotation, \@cut_aa, $cut_term, \@inhibition_aa);
	
	#
	# Process peptides.
	#
	foreach my $peptide_with_context (sort(keys(%{$peptides}))) {
		
		#
		# Get peptide properties.
		#
		$logger->debug('Peptide with context: ' . $peptide_with_context);
		my ($bare_peptide) = _ParsePeptide($peptide_with_context);
		my $peplength = length($bare_peptide);				
		my ($pepweight) = _MwCalc($bare_peptide);
		
		#
		# Apply filters
		#
		# Filter 1 is on weight.
		#
		if (defined($min_peptide_weight)) {
			
			$logger->debug('Minimum weight filter:');
			$logger->debug("\t" . 'Peptide weight: ' . $pepweight);
			
			if ($pepweight >= $min_peptide_weight) {
				
				$logger->debug("\t" . 'PASSED   - Weight is >= ' . $min_peptide_weight);
				
			} else {
				
				# Skip this one.
				$logger->debug("\t" . 'REJECTED - Weight is < ' . $min_peptide_weight);
				next;
				
			}
		}
		
		if (defined($max_peptide_weight)) {
			
			$logger->debug('Maximum weight filter:');
			$logger->debug("\t" . 'Peptide weight: ' . $pepweight);
			
			if ($pepweight <= $max_peptide_weight) {
				
				$logger->debug("\t" . 'PASSED   - Weight is <= ' . $max_peptide_weight);
				
			} else {
				
				# Skip this one.
				$logger->debug("\t" . 'REJECTED - Weight is > ' . $max_peptide_weight);
				next;
				
			}
		}
					
		#
		# Filter 2 is on sequence motifs.
		#
		if (scalar(@filters) > 0) {
			
			$logger->debug('Motif filter:');
			my ($motif) = _ContainsMotif($bare_peptide, \@filters);
			
			if ($motif > 0) {
				
				$logger->debug("\t" . 'PASSED   - Peptide contains motif ' . $motif);
				
			} else {
				
				# Skip this one.
				$logger->debug("\t" . 'REJECTED - Peptide does not contain any motif.');
				next;
				
			}
		}
		
		my ($pepPI)		= _PiCalc($bare_peptide);
		my ($pepCharge)	= _ChargeCalc($bare_peptide);
			
		#
		# Filter 3 is on the amount of charges.
		#
		if (defined($max_charge)) {
			
			$logger->debug('Charge filter:');
			$logger->debug("\t" . 'Peptide charge: ' . $pepCharge);
			
			if (defined($max_charge) && $pepCharge <= $max_charge) {
					
				$logger->debug("\t" . 'PASSED   - Charge <= ' . $max_charge);
				
			} else {
				
				# Skip this one.
				$logger->debug("\t" . 'REJECTED - Charge > ' . $max_charge);
				next;
				
			}
		}
		
		#
		# If there is no partial digestion we can calculated the % coverage.
		#
		unless ($partial_cleavage) {
			$total_peptide_length += length($bare_peptide);
		}
		
		my ($residue_count) = _CountResiduesSTY($bare_peptide);
		
		#
		# Store peptide.
		#
		my $pep_sequence;
		
		if ($add_sequence_context) {
			$pep_sequence = $peptide_with_context;
		} else {
			$pep_sequence = $bare_peptide;
		}
		
		print($output_fh $id . "\t" . $pep_sequence . "\t" . $pepweight . "\t" . $pepPI. "\t" . $pepCharge. "\t" . $residue_count . "\n");
		
	}
	
	#
	# If partial digestion was not enabled, we can calculated the % coverage.
	#
	unless ($partial_cleavage) {
			my $coverage = ($total_peptide_length / $total_length_sequence)*100;
			$logger->debug("Sequence residues: $total_length_sequence | #peptide residues: $total_peptide_length | %Coverage: $coverage");            
	}
}

sub _ParseHeader {
	
	my ($header) = @_;
	my %annotation;
	my $ids;
	my $id;
	my $description;
	
	$header=~ s/^>//;
	
	if ($header =~ m/([^\s]+)\s+([^\s]+.*)/) {
		$ids = $1;
		$description = $2;
	} else {
		$ids = $header;
	}
	
	#
	# Redimentory support for detecting multiple IDs: check for pipe sperated IDs.
	#
	if ($ids =~ m/([^\|])\|/) {
		$id = $1;
	} else {
		$id = $ids;
	}
	
	$annotation{'ID'} = $id;
	$annotation{'DE'} = $description;
	
	return (\%annotation);
	
}

sub _ContainsMotif{
	
	my ($peptide, $filters) = @_;
	my $cnt = 0;
	
	foreach my $filter (@{$filters}){
		
		$cnt++;
		if ($peptide =~ /$filter/){
			return($cnt);
		}	
	
	}
	
	return(0);

}

sub _ParsePeptide{
	
	my ($peptide_with_flanking_context) = @_;
	
	my @pep = split(/\./, $peptide_with_flanking_context);
	my $bare_peptide = uc($pep[1]);
	
	return($bare_peptide);	
	
}

sub _Digest{
	
	my ($sequence, $annotation, $enz_cutting, $cut_term, $enz_restrict) = @_;
	
	$sequence = uc($sequence);
	my %pept = ();

	# we start by scanning the sequence.. to find one of the cutting rulez not followed by a restict rule
	# what is the sequence length
	my @array = split(//, $sequence);
	my $length = scalar(@array);
	my $start_offset = 0;
	my $offset_adjust_for_cleavage_terminus = 0;
	if ($cut_term eq 'n') {
		$offset_adjust_for_cleavage_terminus = 1;
	}
	
	my $peptide = '';
	
	my $counter = 1;
	if (!($partial_cleavage)) {
		$partial_cleavage_chance = 0;
	} else {
		$counter = 100;
	}
	
	#this is for incomplete cleavage... we repeat digest 100 times with a probability that the enzyme will not cut
	for (my $cnt = 0; $cnt < $counter; $cnt++) {
		
		AA:for (my $aa_offset = 0 + $offset_adjust_for_cleavage_terminus; $aa_offset < ($length - 1 + $offset_adjust_for_cleavage_terminus); $aa_offset++) {
			
			my $this_aa = substr($sequence, $aa_offset, 1);
			
			#
			# Check if protease recognizes this amino acid as cleavage site.
			#
			foreach my $cut_aa (@{$enz_cutting}) {
				
				if ($this_aa eq $cut_aa) {
									
					#
					# Check if AA is not preceeded or followed by an AA that inhibits the protease... 
					#
					foreach my $inhibit (@{$enz_restrict}) {
						 

						my @inhibit_conditions = split(/=/, $inhibit);
						my $inhibit_aa = $inhibit_conditions[0];
						my $position_to_check = $inhibit_conditions[1];
						
						my $neighborhood_aa = substr($sequence, $aa_offset + $position_to_check, 1);
												
						if ($neighborhood_aa eq $inhibit_aa){
							$logger->debug('No cleavage due to inhibition by ' . $inhibit_aa . ' at position ' . $position_to_check);
							next AA;
						}
					}
					
					#
					# Consider the possibility of not cutting when doing incomplete digestions!
					#
					my $random = 1;
					if ($partial_cleavage){
						$random = rand(1);
					}
					if ($random <= $partial_cleavage_chance){
						$logger->debug('No cleavage due to incomplete digestion.');
						next AA;
					}
					
					#
					# If no inhibition spoiled the cleavage, lets cut! 
					#
					my $cut_offset;
					if ($cut_term eq 'c') {
						$cut_offset = $aa_offset + 1;
					} elsif ($cut_term eq 'n') {
						$cut_offset = $aa_offset;
					}
					
					# nice formatting of peptide
					if ($start_offset == 0){
						$peptide .="terminus.";
						$peptide .= substr($sequence, $start_offset, $cut_offset - $start_offset).".";
					}else{
						$peptide .= substr($sequence, $start_offset - 3, 3).".";
						$peptide .= substr($sequence, $start_offset, $cut_offset - $start_offset).".";
					}
					$peptide .= substr($sequence, $cut_offset, 3);
					$start_offset = $cut_offset;
					
					# check if peptide already exists
					# if so, concatenate this fasta header 
					#if (exists($pept{$peptide})){
					#	$fasta_header .= $pept{$peptide};
					#}
					$pept{$peptide} = ${$annotation}{'ID'};
					$peptide = '';
				}
			}
		}
		
		#
		# The last peptide sequence !
		#
		$peptide = substr($sequence, $start_offset - 3, 3).".";
		$peptide .= substr($sequence, $start_offset, $length);
		$peptide .= ".terminus";
		$pept{$peptide} = ${$annotation}{'ID'};
		
	} #COUNT
	
	return(\%pept);
	
}

sub _PiCalc{
	
	my ($sequence) = @_;
	
	my $nTermResidue;
	my $cTermResidue;
	my $phMin;my $phMid ;my $phMax;
	my $charge;
	my $cter; my $nter; my $carg; my $chis; my $clys;my $casp;my $cglu;my $ccys;my $ctyr;
	
	my $composition = _GetComposition($sequence);
	my $strlength = length($sequence);
	$nTermResidue = substr($sequence, 0, 1);
	for ($nTermResidue){s/[\s\n\r\t]//g;};
	$cTermResidue = substr($sequence, $strlength - 1, 1);
	for ($cTermResidue){s/[\s\n\r\t]//g;};
	$phMin = $PH_MIN;
	$phMax = $PH_MAX;
	my $i;
	
	for ($i=0, $charge = 1.0; $i<$MAXLOOP && ($phMax-$phMin)>$EPSI; $i++){
		$phMid = $phMin + ($phMax - $phMin) / 2;
		$cter = 10**(-$cPk{$cTermResidue}->[0]) / (10**(-$cPk{$cTermResidue}->[0]) + 10**(-$phMid));	
		$nter = 10**(-$phMid)/(10**(-$cPk{$nTermResidue}->[1])+10**(-$phMid));
		
		$carg = ${$composition}{R} * 10**(-$phMid) / (10**(-$cPk{'R'}->[2])+10**(-$phMid));
		$chis = ${$composition}{H} * 10**(-$phMid) / (10**(-$cPk{'H'}->[2])+10**(-$phMid));
		$clys = ${$composition}{K} * 10**(-$phMid) / (10**(-$cPk{'K'}->[2])+10**(-$phMid));
		
		$casp = ${$composition}{D} * 10**(-$cPk{'D'}->[2]) / (10**(-$cPk{'D'}->[2])+10**(-$phMid));
		$cglu = ${$composition}{E} * 10**(-$cPk{'E'}->[2]) / (10**(-$cPk{'E'}->[2])+10**(-$phMid));
		
		$ccys = ${$composition}{C} * 10**(-$cPk{'C'}->[2]) / (10**(-$cPk{'C'}->[2])+10**(-$phMid));
		$ctyr = ${$composition}{Y} * 10**(-$cPk{'Y'}->[2]) / (10**(-$cPk{'Y'}->[2])+10**(-$phMid));
		
		$charge = $carg + $clys + $chis + $nter - ($casp + $cglu + $ctyr + $ccys + $cter);
		
		if ($charge > 0.0){
			$phMin = $phMid;	
		}else{
			$phMax = $phMid;
		}
	}
	
	return($phMid);
	
}
 
sub _MwCalc{
	
	my ($sequence) = @_;
	
	my $mw;
	my $strlength = length($sequence);
	my $composition = _GetComposition($sequence);
		
	# subtract N-1 water molecules
	$mw = - ($strlength -1) * $H20;
	
	foreach my $aa (sort keys %{$composition}){
		$logger->trace('AA:' . $aa . ' | frequency: ' . ${$composition}{$aa} . ' | AA MW: ' . $cMWs{$aa});
		$mw += ${$composition}{$aa} * $cMWs{$aa};	
	}
	
	return($mw);
	
}

sub _ChargeCalc{
	
	my ($sequence) = @_;
	
	my $charge;
	my $composition = _GetComposition($sequence);
	
	foreach my $aa (sort(keys(%{$composition}))){
		$charge += ${$composition}{$aa} * $charges{$aa};	
	}
	
	return($charge);
	
}

sub _CountResiduesSTY{
	
	my ($sequence) = @_;
	
	my $composition = _GetComposition($sequence);
	my $sty_residues = ${$composition}{'S'} . "\t" . ${$composition}{'T'} . "\t" . ${$composition}{'Y'};
	
	return($sty_residues);
	
}

sub _GetComposition {
	
	my ($sequence) = @_;	
	
	my $i;
	my $c;
	my %composition = ('A'=>0, 'B'=>0,'C'=>0, 'D'=>0, 'E'=>0, 'F'=>0,'G'=>0, 'H'=>0, 'I'=>0,
				'J'=>0, 'K'=>0,'L'=>0, 'M'=>0, 'N'=>0, 'O'=>0,'P'=>0, 'Q'=>0, 'R'=>0,
				'S'=>0, 'T'=>0,'U'=>0, 'V'=>0, 'W'=>0, 'X'=>0,'Y'=>0, 'Z'=>0);	
	
	#
	# Compute aminoacid composition.
	#
	my $strlength = length($sequence);
	for ($i=0; $i<$strlength; $i++){
		$c = substr($sequence, $i, 1);
		$composition{$c}++;
	}
	
	return(\%composition);
	
}

sub _Usage {
	
	my $longest_enzyme_name_length = 0;
	foreach my $protease (keys(%enzymes)) {
		if (length($protease) > $longest_enzyme_name_length) {
			 $longest_enzyme_name_length = length($protease);
		}
	}
	my $field_formatting = '%-' . ($longest_enzyme_name_length + 3) . 's';
	
	print "\n";
	print "ProteinDigestor.pl - Digests protein sequences from a FASTA file\n";
	print "\n";
	print "Usage:\n";
	print "\n";
	print "   ProteinDigestor.pl options\n";
	print "\n";
	print "Available options are:\n";
	print "\n";
	print "   -i [file]          Input FASTA file.\n";
	print "   -o [file]          Output stats file.\n";
	print "\n";
	print "                      You can either specify a protease this tool knows with -e\n";
	print "                      or you can specify the cleavage rule for a protease this does not know (yet) with -r\n";
	print "\n";
	print "   -e [enzyme_name]   Digestion enzyme. Known enzymes and their cleavage rules:\n";
	
	foreach my $protease (sort(keys(%enzymes))) {
		print '                         ' . sprintf("$field_formatting", $protease) . $enzymes{$protease} . "\n";
	}
	
	print "   -r [enzyme_rule]   Protease cleavage site rule. This rule contains sperated by colons:\n";
	print "                         * The terminus that indicates on which side of a recognized amino acid the protease will cleave: c or n.\n";
	print "                         * The amino acids recognized by the protease.\n";
	print "                           Multiple amino acids separated by a comma.\n";
	print "                         * The amino acids that inhibit cleavage and their position relative to amino acids recognized by the protease.\n";
	print '                           Amino acid and its relative position separated by an equals sign (=).' . "\n";
	print "                           Multiple amino acids separated by a comma.\n";
	print '                         For example \'c:K,R:P=1\' for Trypsin with proline inhibition.' . "\n";
	print "   -s                 Semi for partial digestion.\n";
	print "   -p [chance]        Number between 0 and 1 indicating the chance that a site will not be cleaved.\n";
	print "   -m [weight]        Minimum weight for a peptide.\n";
	print "   -n [weight]        Maximum weight for a peptide.\n";
	print "   -c [int]           Maximum charge a peptide is allowed to have.\n";
	print "   -a                 Add sequence context.\n";
	print "                      This will add max 3 amino acids or the word terminus on each side of the peptides.\n";
	print "                      Contexts and peptides are separated with a dot.\n";
	print "                      Examples of peptides with a context:\n";
	print "                         terminus.MSVSLSAK.ASH\n";
	print "                         SAK.ASHLLCSSTR.VSL\n";
	print "                         STR.VSLSPAVTSSSSSPVVRPALSSSTS.terminus\n";
	print "   -l [LEVEL]         Log4perl log level. One of: ALL, TRACE, DEBUG, INFO (default), WARN, ERROR, FATAL or OFF.\n";
	print "\n";
	exit;
	
}