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  • Title: Role of N-terminal domain of streptokinase in protein transport.
    Author: Pratap J, Kaur J, RajaMohan G, Singh D, Dikshit KL.
    Journal: Biochem Biophys Res Commun; 1996 Oct 03; 227(1):303-10. PubMed ID: 8858140.
    Abstract:
    Streptokinase (SK), an extracellular protein of several haemolytic strains of Streptococcus, is utilized as a potent thrombolytic agent for the treatment of various myocardial disorders. Functional properties of SK remain unchanged when the first 13 N-terminal amino acid (aa) residues are removed. At present, role of this segment in protein structure function is unclear. skc gene encoding for the mature SK and its deletion variant, lacking its first 13 aa residues, were cloned and expressed in E. coli. Full length SK, deprived of any leader sequences, was able to translocate slowly, across the cyto-plasmic and outer membranes of E.coli. Whereas, SK derivative, devoid of its first 13 N-terminal aa residues, could not do so. Cell fractionation studies as well as genetic evidences utilizing alkaline phosphatase fusion, point towards the existence of additional information for protein transport, within the N-terminal domain of SK. To further investigate the role of this region in protein secretion, genetic fusions were created in between full length and 13 aa deleted SK with OmpA leader peptide. Studies on kinetics of SK export from E.coli, revealed that translocation of protein is 3-4 times faster when the first 13 N-terminal residues of SK are intact. On the basis of results obtained, it has been proposed that the N-terminus of mature SK maintains the export competent status of protein and, thus, confer speed and efficiency upon the translocation process of streptokinase.
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