This would be a neat excuse to use negative array indexes subscripts. The split is probably not the utmost in efficiency, but it's pretty easy to write, and easier for others to understand...

#!/usr/bin/perl
use strict;

while (<DATA>) {
    my @nodes = split ('/');
    print $nodes[-1];
}

__DATA__
/home/users/me/proteins/1hc9.txt
/home/users/me/proteins/193l.txt
/home/users/me/proteins/1trz.txt
/home/users/me/proteins/2psg.txt
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