BtrH_N is the N-terminus of the acyl carrier protein:aminoglycoside acyltransferase BtrH. Alternatively it can be referred to as butirosin biosynthesis protein H. BtrH transfers the unique (S)-4-amino-2-hydroxybutyrate (AHBA) side chain, which protects the antibiotic butirosin from several common resistance mechanisms. Butirosin, an aminoglycoside antibiotic produced by Bacillus circulans, exhibits improved antibiotic properties over its parent molecule and retains bactericidal activity toward many aminoglycoside-resistant strains. Butirosin is unique in carrying the AHBA side-chain. BtrH transfers the AHBA from the acyl carrier protein BtrI to the parent aminoglycoside ribostamycin as a gamma-glutamylated dipeptide [1,2].

1: Extended sequence and functional analysis of the butirosin biosynthetic gene cluster in Bacillus circulans SANK 72073. Kudo F, Numakura M, Tamegai H, Yamamoto H, Eguchi T, Kakinuma K; J Antibiot (Tokyo). 2005;58:373-379. PMID:16156513

2: Structural and biochemical studies elucidate the mechanism of rhamnogalacturonan lyase from Aspergillus aculeatus. Jensen MH, Otten H, Christensen U, Borchert TV, Christensen LL, Larsen S, Leggio LL; J Mol Biol. 2010;404:100-111. PMID:20851126