It might be easier to split the line on white space and slice out the relevant items.

johngg@shiraz:~/perl/Monks$ perl -Mstrict -Mwarnings -E '
open my $inFH, q{<}, \ <<__EOD__ or die $!;
BOGUS PPI3_SYNY3 276 aa linear BCT 13-NOV-2019
__EOD__

chomp( my $line = <$inFH> );
close $inFH or die $!;

my( $bogus, $acids ) = ( split m{\s+}, $line )[ 1, 2 ];
say qq{Bogus                 : $bogus\nNumber of amino acids : $acids}
+;'
Bogus                 : PPI3_SYNY3
Number of amino acids : 276
[download]

I hope this is helpful.