DB<10> p $p
ALTAMCMNVWEITYHKGSDVNRRASFAQPPPQPPPPLLAIKPASDASD
  DB<11> $p = 'ALTAMCMNVWEITYHKGSDVNRRASFAQPPPQPPPPLLAIKPASDASD';

  DB<12> $p =~ s/([KR])(?!P)/$1=/g;

  DB<21> p $p
ALTAMCMNVWEITYHK=GSDVNR=R=ASFAQPPPQPPPPLLAIKPASDASD