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Identiﬁcation and characterization of b -lactamase inhibitor protein-II (BLIP-II) interactions with b -lactamases using phage display

Protein–protein interactions are critical to cellular processes yet the ability to predict and rationally design interactions is limited because of incomplete knowledge of the principles governing these interactions. The b -lactamase inhibitory protein (BLIP)/ b -lactamase interaction has become a model system to investigate protein– protein interactions and has been the focus of several structural, thermodynamic and binding speciﬁcity studies. BLIP-II also inhibits b -lactamase but has no sequence homology with BLIP. The structure of BLIP-II in complex with TEM-1 b -lactamase revealed that BLIP-II has a completely different structure than BLIP but it interacts with the same protruding loop-helix region of TEM-1 as does BLIP. The signiﬁcance of the individual interacting residues in molecular recognition by BLIP-II is currently unknown. Therefore, a phage display vector was developed with the purpose of expressing BLIP-II onto the surface of the M13 ﬁlamentous bacteriophage. The BLIP-II displayed phage bound to TEM-1 with picomolar afﬁnity indicating that BLIP-II is properly folded while on the surface of the phage. The phage system, as well as enzyme inhibition assays with puriﬁed proteins, revealed that BLIP-II is a more potent inhibitor than BLIP for several class A b -lactamases with K i values in the low picomolar range.