The binding site on the lymphocyte function-associated antigen-1 (LFA-1) of a class of hydantoin-based antagonists of leukocyte cell adhesion has been identified. This site resides in the inserted-domain (I-domain) of the CD11a chain at a location that is distal to residues known to be required for interactions with the intercellular adhesion molecules. This finding supports the hypothesis that the molecules are antagonizing cell adhesion via an allosteric modification of LFA-1. The binding site was identified using an integrated immunochemical, chemical, and molecular modeling approach. Antibodies that map to epitopes on the I-domain were blocked from binding to the purified protein by the hydantoins, indicating that the hydantoin-binding site resides on the I-domain. Photoaffinity labeling of the I-domain followed by LC/MS and LC/MS/MS analysis of the enzymatic digest identified proline 281 as the primary amino acid residue covalently attached to the photoprobe. Distance constraints derived from this study coupled with known SAR considerations allowed for the construction of a molecular model of the I-domain/inhibitor complex. The atomic details of the protein/antagonist interaction were accurately predicted by this model, as subsequently confirmed by the X-ray crystal structure of the complex.

The specificity of the immune response relies on processing of foreign proteins and presentation of antigenic peptides at the cell surface. Inhibition of antigen presentation, and the subsequent activation of T-cells, should, in theory, modulate the immune response. The cysteine protease Cathepsin S performs a fundamental step in antigen presentation and therefore represents an attractive target for inhibition. Herein, we report a series of potent and reversible Cathepsin S inhibitors based on dipeptide nitriles. These inhibitors show nanomolar inhibition of the target enzyme as well as cellular potency in a human B cell line. The first X-ray crystal structure of a reversible inhibitor cocrystallized with Cathepsin S is also reported.

Recent reports have demonstrated the potential of monocyclic β-lactam derivatives as inhibitors of human cytomegalovirus (HCMV) protease. Investigation of the mechanism of inhibition by NMR and mass spectrometry has revealed the presence of an acylenzyme intermediate suggesting that β-lactams are hydrolyzed by the enzyme and cause inhibition by competing with substrate. The potential of a fluorogenic β-lactam derivative for convenient kinetic characterization of this mechanism has been evaluated using 4S-(4-methylumbelliferone)-3R-methylazetidin-2-one-1-carboxylic acid (4-methylpyridyl) amide (1). Upon acylation of the enzyme, the fluorescent umbelliferone moiety is released, allowing for continuous monitoring of the hydrolytic process. Examination of a series of progress curves by numerical analysis has provided valuable information on acylation and deacylation rates which relate to the IC50 values observed for β-lactams. More importantly the potential of compound 1 as an active site titrating agent for HCMV protease has been exploited, and a simple protocol for rapid determination of active enzyme is described. The data are consistent with the HCMV protease dimer being composed of two functional active sites. This titrating agent represents an important tool that should significantly facilitate the characterization of this novel enzyme.

A platelet-fibrinogen-thrombin mixture utilizing autologous platelets was studied for its potential to seal perforating corneal wounds. In rabbits, the mixture demonstrated sufficient adhesive properties to permit 75% of penetrating keratoplasties to remain in place without the use of sutures. All 12 grafts held initially; after 48 h three grafts extruded. In control eyes only two out of 12 (16%) of the corneal grafts remained in place. The material is simple to prepare and apply and is not toxic to the cornea. It does not cause inflammation or lid irritation. Intraocular complications observed with its use were transient anterior synechiae and retrocorneal membrane formation.