Hi sanku, First thing is look into How (Not) To Ask A Question and How do I post a question effectively?, then you try like this,

use strict;
use warnings;

my $str = 'MKTVEQTSPTMTSEKARWIYQKMVEIRMFEDRVHDIFSKGEIPGFVHLYAGEEAIAVGL
+CAHLDHNDYITSTHRGHGHCIAKGCELDGMMAEIYGKSTGLCKGKGGSMHIADLDRGMLGANGIVGGGF
+TLAAGAALTAKFKQTGGVAVCFFGDGANNQGTFHEGINLAAIWDLPVVFVAENNGYGEATPFHYASACE
+QITDRAKGYNIPGVKVDGKDVVAVYEVAREAVERARRGEGPTLIECITYRNYGHFEGDAQTYKTGREKE
+EHTEERDAITLFEKYALSNNLLTEEAIQTVRHEVEQSVDRAVDFANASDYPQPEELLTDVYVSYDHEGR
+NG';

$str =~ s/(.{10})/$1 /gsi;
$str =~ s/((?:[^ ]+ ){5})/$1\n/gsi;

print $str;
[download]

davorg++

Updated : Thanks BrowserUK