Involved in the biosynthesis of a unique class of isonitrile lipopeptides (INLPs). Catalyzes a Michael addition of glycine to the beta-position of an alpha,beta-unsaturated fatty acyl-[ACP], producing a (3R)-3-[(carboxymethyl)amino]fatty acid. Acts on the (2E)-butenoyl moiety loaded on the acyl-carrier protein ScoB, forming the product (3R)-3-[(carboxymethyl)amino]butanoate released from ScoB