Properties of a Novel PBP2A Protein Homolog from Staphylococcus aureus Strain LGA251 and Its Contribution to the beta-Lactam-resistant Phenotype

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Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) strains show strain-to-strain variation in resistance level, in genetic background, and also in the structure of the chromosomal cassette (SCCmec) that carries the resistance gene mecA. In contrast, strain-to-strain variation in the sequence of the mecA determinant was found to be much more limited among MRSA isolates examined so far. The first exception to this came with the recent identification of MRSA strain LGA251, which carries a new homolog of this gene together with regulatory elements mecI/mecR that also have novel, highly divergent structures. After cloning and purification in Escherichia coli, PBP2A(LGA), the protein product of the new mecA homolog, showed aberrant mobility in SDS-PAGE, structural instability and loss of activity at 37 degrees C, and a higher relative affinity for oxacillin as compared with cefoxitin. The mecA homolog free of its regulatory elements was cloned into a plasmid and introduced into the background of the beta-lactam-susceptible S. aureus strain COL-S. In this background, the mecA homolog expressed a high-level resistance to cefoxitin (MIC = 400 mu g/ml) and a somewhat lower resistance to oxacillin (minimal inhibitory concentration = 200 mu g/ml). Similar to PBP2A, the protein homolog PBP2A(LGA) was able to replace the essential function of the S. aureus PBP2 for growth. In contrast to PBP2A, PBP2A(LGA) did not depend on the transglycosylase activity of the native PBP2 for expression of high level resistance to oxacillin, suggesting that the PBP2A homolog may preferentially cooperate with a monofunctional transglycosylase as the alternative source of transglycosylase activity.
Original languageUnknown
Pages (from-to)36854-36863
JournalJournal of Biological Chemistry
Volume287
Issue number44
DOIs
Publication statusPublished - 1 Jan 2012

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