$pattern = LP[SKTAQEHLDN][TA][GN][EDASTV] = 5/6

##</code><code>##

#!/usr/bin/perl -wl
use strict;

while (my $string = <DATA>) {
    chomp($string);
    my @matches = $string =~ /(L)?(P)?([SKTAQEHLDN])?([TA])?([GN])?([EDASTV])?/;

    my $num_matches;
    for (@matches) {
        $num_matches++ if defined($_);
    }

    if ($num_matches > 4) {
        print "$string matches ($num_matches/6)";
    }
    else {
        print "$string does not match ($num_matches/6)";
    }
}

__DATA__
LPSTEOPRTRYERTRETR
HELLO WORLD
PERL MONKS

##</code><code>##

LPSTEOPRTRYERTRETR matches (5/6)
HELLO WORLD does not match (2/6)
PERL MONKS does not match (2/6)