The effects of plasma proteins on controlling the activity of matrix metalloproteinases (MMPs, matrixins) have been the focus of numerous studies, although only a few have examined the influence of matrixins on plasma proteins. Recently, it has been shown that MMPs may play a role in the degradation of fibrin. We have now investigated the role of collagenase-2 (MMP-8), macrophage elastase (MMP-12), collagenase-3 (MMP-13), and membrane type 1-matrix metalloproteinase (MT1-MMP, MMP-14) in the degradation of fibrinogen and Factor XII of the plasma clotting system. Our data demonstrate that the catalytic domains of MMP-8, MMP-12, MMP-13, and MMP-14 can proteolytically process fibrinogen and, with the exception of MMP-8, also inactivate Factor XII (Hageman factor). We have identified the amino termini of the major protein fragments. Cleavage of fibrinogen occurred in all chains and resulted in significantly impaired clotting. Moreover, rapid proteolytic inactivation of Factor XII (Hageman factor) by MMP-12, MMP-13, and MMP-14 was noted. These results support the hypothesis of an impaired thrombolytic potential of MMP-degraded Factor XII in vivo. MMPinduced degradation of fibrinogen supports a plasminindependent fibrinolysis mechanism. Consequently, degradation of these proteins may be important in inflammation, atherosclerosis, and angiogenesis, all of which are known to be influenced by MMP activity.The matrix metalloproteinases, MMPs 1 and matrixins, form a family of structurally and functionally related zinc-containing endopeptidases. Together they are able to degrade most of the constituents of the extracellular matrix such as basement membrane, collagens, proteoglycans, fibronectin, and laminin (1). Thus, they are implicated in connective tissue remodeling processes associated with embryonic development, pregnancy, growth, and wound repair (2). The deleterious potential of the MMPs is normally controlled by the endogenous and specific tissue inhibitors of metalloproteinases or the more general nonspecific ␣ 2 -macroglobulin (3). Disturbance of the well balanced equilibrium of MMPs and tissue inhibitors of metalloproteinases results in pathological situations such as rheumatoid and osteoarthritis, atherosclerosis, tumor growth, metastasis, and fibrosis (4-8). In addition to degradation of extracellular matrix constituents, plasma proteins such as serpins (9) or fibrinogen and cross-linked fibrin (10-12) are also cleaved.Fibrinogen is a 340-kDa dimeric glycoprotein consisting of a pair of three polypeptide chains A␣, B␤, and ␥ that are interconnected by 29 disulfide bonds. The amino termini of these chains are joined together in a central domain that can be isolated as a single fragment from a plasmin digestion of fibrinogen (13). During blood coagulation, fibrinogen participates in both the cellular phase and the fluid phase of blood clot formation (14, 15). Fibrinogen can be converted into an insoluble fibrin clot as a consequence of thrombin-catalyzed removal of fibrinopeptides A (FpA, A␣-(20 -35)) 2 and B (FpB...

Potent and selective inhibitors of matrix metalloproteinases (MMPs), a family of zinc proteases that can degrade all the components of the extracellular matrix, could be useful for treatment of diseases such as cancer and arthritis. The most potent MMP inhibitors are based on hydroxamate as zinc-binding group (ZBG). alpha-Arylsulfonylamino phosphonates incorporate a particularly favorable combination of phosphonate as ZBG and arylsulfonylamino backbone so that their affinity exceptionally attains the nanomolar strength frequently observed for hydroxamate analogues. The detailed mode of binding of [1-(4'-methoxybiphenyl-4-sulfonylamino)-2-methylpropyl]phosphonate has been clarified by the crystal structures of the complexes that the R- and S-enantiomers respectively form with MMP-8. The reasons for the preferential MMP-8 inhibition by the R-phosphonate are underlined and the differences in the mode of binding of analogous alpha-arylsulfonylamino hydroxamates and carboxylates are discussed.

The online version of this article has a Supplementary Appendix. BackgroundPolymorphic differences between donor and recipient human leukocyte antigen class I molecules can result in graft-versus-host disease due to distinct peptide presentation. As part of the peptide-loading complex, tapasin plays an important role in selecting peptides from the pool of potential ligands. Class I polymorphisms can significantly alter the tapasin-mediated interaction with the peptide-loading complex and although most class I allotypes are highly dependent upon tapasin, some are able to load peptides independently of tapasin. ). From these alleles, only the high tapasin-dependency of human leukocyte antigen B*44:02 has been reported. Design and MethodsWe investigated the influence of position 156 polymorphisms on both the requirement of tapasin for efficient surface expression of each allotype and their peptide features. Genes encoding human leukocyte antigen B*44 variants bearing all possible substitutions at position 156 were lentivirally transduced into human leukocyte antigen class I-negative LCL 721.221 cells and the tapasin-deficient cell line LCL 721.220. ResultsExclusively human leukocyte antigen B*44:28 156Arg was expressed on the surface of tapasin-deficient cells, suggesting that the remaining B*44/156 variants are highly tapasin-dependent. Our computational analysis suggests that the tapasin-independence of human leukocyte antigen B*44:28 156Arg is a result of stabilization of the peptide binding region and generation of a more peptide receptive state. Sequencing of peptides eluted from human leukocyte antigen B*44 molecules by liquid chromatography-electrospray ionization-mass spectrometry (LTQOrbitrap) demonstrated that both B*44:02 and B*44:28 share the same overall peptide motif and a certain percentage of their individual peptide repertoires in the presence and/or absence of tapasin. ConclusionsHere we report for the first time the influence of position 156 on the human leukocyte antigen/ tapasin association. Additionally, the results of peptide sequencing suggest that tapasin chaperoning is needed to acquire peptides of unusual length.Key words: HLA polymorphism, peptide-loading complex, tapasin, peptide-binding motif.Citation: Badrinath S, Saunders P, Huyton T, Aufderbeck S, Hiller O, Blasczyk R, and Bade-Doeding C. Position 156 influences the peptide repertoire and tapasin dependency of human leukocyte antigen B*44 allotypes. Haematologica 2012;97(1):98-106. doi:10.3324/haematol.2011

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