FabB1

fabB1 is a gene encoding a beta-ketoacyl-ACP synthase I (KAS I) family enzyme involved in type II fatty acid synthesis in bacteria. When present with other paralogs, such as fabB2, fabB1 is typically the principal enzyme responsible for elongating fatty acyl chains during phospholipid biosynthesis. The product of fabB1 contributes to the formation of long-chain fatty acids that become components of the bacterial membrane.

In organisms that harbor multiple fabB-like genes, fabB1 often operates within the fatty acid synthesis II operon, alongside other core enzymes of the pathway. The presence of a fabB1 paralog can confer substrate flexibility or regulatory nuance, allowing bacteria to adapt fatty acid production to growth conditions or environmental stresses. The exact physiological role and substrate preference of fabB1 can vary among species and strains.

Biochemically, the enzyme is a condensing enzyme that catalyzes the Claisen-like condensation of malonyl-ACP with an acyl-ACP primer, extending the fatty acyl chain by two carbon units. It belongs to the ketoacyl synthase family and uses an active-site cysteine to form a transient acyl-enzyme intermediate during catalysis. Regulation of fabB1 expression and activity often reflects cellular fatty acid demand and the status of membrane lipid synthesis.

FabB1 is relevant to studies of bacterial lipid metabolism and has been discussed as a potential target for antimicrobial development, given its essential role in membrane biogenesis in many bacteria. Variation in the gene’s presence and regulation across species underlies differing fatty acid biosynthesis strategies.