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|
2006
|
vol. 53
|
issue 4
617-626
EN
A number of antiviral lectins, small proteins that bind carbohydrates found on viral envelopes, are currently in pre-clinical trials as potential drugs for prevention of transmission of human immunodeficiency virus (HIV) and other enveloped viruses, such as the Ebola virus and the coronavirus responsible for severe acute respiratory syndrome (SARS). Lectins of algal origin whose antiviral properties make them candidate agents for prevention of viral transmission through topical applications include cyanovirin-N, Microcystis viridis lectin, scytovirin, and griffithsin. Although all these proteins exhibit significant antiviral activity, their structures are unrelated and their mode of binding of carbohydrates differs significantly. This review summarizes the current state of knowledge of the structures of algal lectins, their mode of binding of carbohydrates, and their potential medical applications.
EN
Sedolisins (serine-carboxyl peptidases) are proteolytic enzymes whose fold resembles that of subtilisin; however, they are considerably larger, with the mature catalytic domains containing approximately 375 amino acids. The defining features of these enzymes are a unique catalytic triad, Ser-Glu-Asp, as well as the presence of an aspartic acid residue in the oxyanion hole. High-resolution crystal structures have now been solved for sedolisin from Pseudomonas sp. 101, as well as for kumamolisin from a thermophilic bacterium, Bacillus novo sp. MN-32. The availability of these crystal structures enabled us to model the structure of mammalian CLN2, an enzyme which, when mutated in humans, leads to a fatal neurodegenerative disease. This review compares the structural and enzymatic properties of this newly defined MEROPS family of peptidases, S53, and introduces their new nomenclature.
EN
We carried out chymotryptic digestion of multimeric ATP-dependent Lon protease from Escherichia coli. Four regions sensitive to proteolytic digestion were located in the enzyme and several fragments corresponding to the individual structural domains of the enzyme or their combinations were isolated. It was shown that (i) unlike the known AAA+ proteins, the ATPase fragment (A) of Lon has no ATPase activity in spite of its ability to bind nucleotides, and it is monomeric in solution regardless of the presence of any effectors; (ii) the monomeric proteolytic domain (P) does not display proteolytic activity; (iii) in contrast to the inactive counterparts, the AP fragment is an oligomer and exhibits both the ATPase and proteolytic activities. However, unlike the full-length Lon, its AP fragment oligomerizes into a dimer or a tetramer only, exhibits the properties of a non-processive protease, and undergoes self-degradation upon ATP hydrolysis. These results reveal the crucial role played by the non-catalytic N fragment of Lon (including its coiled-coil region), as well as the contribution of individual domains to creation of the quaternary structure of the full-length enzyme, empowering its function as a processive protease.
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