use strict;
use warnings;

<DATA>;  # ignore first input line

while (my $line = <DATA>) {

    $line =~ s{ \t }{; }xmsg;

    # make output ProteinName field min 4 cols wide, right justified.
    $line =~ s{ \A ([^;]*) (?= ;) }{ sprintf '%4s', $1 }xmse;

    print $line;

    }

exit;

__DATA__
ProteinName	MF1	MF2	MF3
GH1	Growth factor activity	Growth hormone receptor binding	Hormone activity
POMC	G protein-coupled receptor binding	Hormone activity	Signaling receptor binding
THRAP3	ATP binding Source	Nuclear receptor transcription coactivator activity	Phosphoprotein binding