Characterization of a Glucosamine/Glucosaminide N -Acetyltransferase of Clostridium acetobutylicum

Abstract

ABSTRACT Many bacteria, in particular Gram-positive bacteria, contain high proportions of non- N -acetylated amino sugars, i.e., glucosamine (GlcN) and/or muramic acid, in the peptidoglycan of their cell wall, thereby acquiring resistance to lysozyme. However, muramidases with specificity for non- N -acetylated peptidoglycan have been characterized as part of autolytic systems such as of Clostridium acetobutylicum . We aim to elucidate the recovery pathway for non- N -acetylated peptidoglycan fragments and present here the identification and characterization of an acetyltransferase of novel specificity from C. acetobutylicum , named GlmA (for gl ucosa m ine/glucosaminide N - a cetyltransferase). The enzyme catalyzes the specific transfer of an acetyl group from acetyl coenzyme A to the primary amino group of GlcN, thereby generating N -acetylglucosamine. GlmA is also able to N -acetylate GlcN residues at the nonreducing end of glycosides such as (partially) non- N- acetylated peptidoglycan fragments and β-1,4-glycosidically linked chitosan oligomers. K m values of 114, 64, and 39 μM were determined for GlcN, (GlcN) 2 , and (GlcN) 3 , respectively, and a 3- to 4-fold higher catalytic efficiency was determined for the di- and trisaccharides. GlmA is the first cloned and biochemically characterized glucosamine/glucosaminide N -acetyltransferase and a member of the large GCN5-related N -acetyltransferases (GNAT) superfamily of acetyltransferases. We suggest that GlmA is required for the recovery of non- N -acetylated muropeptides during cell wall rescue in C. acetobutylicum .