Labeling of penicillin binding proteins with a photoreactive peptidoglycan peptide analog

Aran, V.; Rodriguez Tebar, A.; Vazquez, D.

Transpeptidases, DD-carboxypeptidases and endopeptidases from bacteria are usually detected by labeling with radioactive .beta.-lactam antibiotics, due to a selective stabilization of the enzyme-antibiotic complex, and are therefore generally known as penicillin-binding proteins (PBP). As a general rule, PBP cannot be detected by labeling with real peptidoglycan substrate analogs other than .beta.-lactams, partly due to the fact that the acyl intermediates formed do not usually accumulate. The chemical synthesis of a radioactive photoreactive derivative of the peptidoglycan substrate L-lysyl-D-alanyl-D-alanine which is able, due to the shortness of its activated state, to label a number of PBP of Escherichia coli by quenching the reaction at the intermediate step, is reported. By using this derivative it was possible to label other PBP of higher MW (190, 170, 146, 125 and 87 kDa [kilodalton]) that were previously detected only by using either photoreactive derivatives of .beta.-lactam or bis-.beta.-lactam or bis-.beta.-lactam antibiotics.