#!/usr/bin/perl

use strict;
use warnings;

my $string = 'DIQMTQSPSSLSASVGDRVTITCXXXXXXXXXXXWYQQKPGKAPKXXXXXXXXXXXGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCXXXXXXXXTFGQGTKVEIK';

my @parts = split /(X+)/, $string;

my $cur_pos = 0;
for my $part ( @parts ) {
    my $start = $cur_pos + 1;
    my $stop  = $cur_pos + length $part;

    print "feature $start .. $stop: $part\n";
    $cur_pos = $stop;
}