4igd | pdb_00004igd
Crystal structure of the zymogen catalytic region of Human MASP-1
Structural highlights
Disease[MASP1_HUMAN] Defects in MASP1 are the cause of 3MC syndrome type 1 (3MC1) [MIM:257920]. 3MC1 is a disorder characterized by facial dysmorphism that includes hypertelorism, blepharophimosis, blepharoptosis and highly arched eyebrows, cleft lip and/or palate, craniosynostosis, learning disability and genital, limb and vesicorenal anomalies. The term 3MC syndrome includes Carnevale, Mingarelli, Malpuech, and Michels syndromes.[1] Function[MASP1_HUMAN] Functions in the lectin pathway of complement, which performs a key role in innate immunity by recognizing pathogens through patterns of sugar moieties and neutralizing them. The lectin pathway is triggered upon binding of mannan-binding lectin (MBL) and ficolins to sugar moieties which leads to activation of the associated proteases MASP1 and MASP2. Functions as an endopeptidase and may activate MASP2 or C2 or directly activate C3 the key component of complement reaction. Isoform 2 may have an inhibitory effect on the activation of the lectin pathway of complement or may cleave IGFBP5.[2] [3] Publication Abstract from PubMedMannan-binding lectin (MBL)-associated serine proteases, MASP-1 and MASP-2, have been thought to autoactivate when MBL/ficolin.MASP complexes bind to pathogens triggering the complement lectin pathway. Autoactivation of MASPs occurs in two steps: 1) zymogen autoactivation, when one proenzyme cleaves another proenzyme molecule of the same protease, and 2) autocatalytic activation, when the activated protease cleaves its own zymogen. Using recombinant catalytic fragments, we demonstrated that a stable proenzyme MASP-1 variant (R448Q) cleaved the inactive, catalytic site Ser-to-Ala variant (S646A). The autoactivation steps of MASP-1 were separately quantified using these mutants and the wild type enzyme. Analogous mutants were made for MASP-2, and rate constants of the autoactivation steps as well as the possible cross-activation steps between MASP-1 and MASP-2 were determined. Based on the rate constants, a kinetic model of lectin pathway activation was outlined. The zymogen autoactivation rate of MASP-1 is approximately 3000-fold higher, and the autocatalytic activation of MASP-1 is about 140-fold faster than those of MASP-2. Moreover, both activated and proenzyme MASP-1 can effectively cleave proenzyme MASP-2. MASP-3, which does not autoactivate, is also cleaved by MASP-1 quite efficiently. The structure of the catalytic region of proenzyme MASP-1 R448Q was solved at 2.5 A. Proenzyme MASP-1 R448Q readily cleaves synthetic substrates, and it is inhibited by a specific canonical inhibitor developed against active MASP-1, indicating that zymogen MASP-1 fluctuates between an inactive and an active-like conformation. The determined structure provides a feasible explanation for this phenomenon. In summary, autoactivation of MASP-1 is crucial for the activation of MBL/ficolin.MASP complexes, and in the proenzymic phase zymogen MASP-1 controls the process. Quantitative characterization of the activation steps of mannan-binding lectin (MBL)-associated serine proteases (MASPs) points to the central role of MASP-1 in the initiation of the complement lectin pathway.,Megyeri M, Harmat V, Major B, Vegh A, Balczer J, Heja D, Szilagyi K, Datz D, Pal G, Zavodszky P, Gal P, Dobo J J Biol Chem. 2013 Mar 29;288(13):8922-34. doi: 10.1074/jbc.M112.446500. Epub 2013, Feb 5. PMID:23386610[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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