Catalyzes the ATP-dependent activation of L-alanine, and to a lesser extent of L-glycine and L-serine, and their transfer to the phosphopantetheine prosthetic group covalently attached to the vicinal carrier protein Atu2571 of yet unknown function. May participate in nonribosomal peptide synthesis or related processes. L-proline and L-glutamate are very poor substrates whereas D-amino acids are not substrates for ATP-dependent activation. Does not display tRNA aminoacylation activity. an L-alpha-amino acid + ATP + holo-[ACP] = AMP + an L-alpha-aminoacyl-[ACP] + diphosphate Binds 1 Zn(2+) ion per subunit. The catalytic efficiency of the alanine activation reaction is 27-fold and 44-fold higher than that of glycine and serine activation, respectively. Homodimer. Lacks the N-terminal tRNA-binding domain compared to class-II aminoacyl-tRNA synthetases. Belongs to the class-II aminoacyl-tRNA synthetase family. Amino acid--[acyl-carrier-protein] ligase subfamily. Truncated N-terminus.