The mechanism of hydrolysis of beta-lactam bond under the impact of albumin

Zhyltsou I.V., Veremey I.S., Semenov V.M., Generalov I.I., Egorov S.K.

The present work is the continuation of our previous investigations of beta-lactamase activity of blood serum and human serum albumin (HSA). We have demonstrated that clavulanic acid and tazobactam inhibit beta-lactamase activity of blood serum and HSA what assumes presence of active site in albumin molecule. HPLC analysis demonstrates that interaction of benzylpenicillin (BP) and albumin leads to formation of two types of complexes followed by complete dissociation of these complexes accompanied by cleavage of BP and release of the single product of its destruction. Computer modeling revealed the binding site in HSA molecule composed by the side chains of the amino acids TYR 148, TYR 150, GLU 153, PHE 157, ARG 160, GLU 188, SER 192, LYS 195, GLN 196, LYS 199, HIS 242, CYS 245, ARG 257, HIS 288, ALA 291, GLU 292, and ASP 451. This active site is responsible for binding of beta-lactam antibiotics and clavulanic acid. Sulbactam and tazobactam bind to HSA molecule in another region composed of amino acids residues PRO 384, LEU 387, ILE 388, ASN 391, GLY 434, ALA 449, and ARG 485. The indirect experimental data were obtained what confirm the existence of the above mentioned active site. The simulated mechanism of catalysis resembles that of serine beta-lactamases of A class. It’s the most likely that side chains of ASP 451 (as electron donor) and ARG 222 (as acceptor) participate in hydrolysis of beta-lactam bond. There is a possibility that the mechanism of hydrolysis differs for different antibiotics.