FIG 2.

In vitro adenylation of E. coli MccA peptide mutants by MccB. Chemically synthesized peptides corresponding to 7-amino-acid-long wild-type MccA MRTGNAN, mutants bearing the indicated single-amino-acid substitutions (underlined), or an MRTGNAN peptide containing a d-stereoisomer of threonine at position 3 were combined with recombinant MccB in the absence (top) and the presence (bottom) of ATP. Reaction products were analyzed by MALDI-MS. The m/z values of mass peaks corresponding to starting peptides and adenylation products are indicated. Adenylation by MccB adds 329 Da to the substrate peptide. Asterisks indicate peaks corresponding to adenylation reaction intermediates containing a terminal succinimide.