• USHA P KAR

      Articles written in Journal of Biosciences

    • Regulation of dynamin family proteins by post-translational modifications

      USHA P KAR HIMANI DEY ABDUR RAHAMAN

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      Dynamin superfamily proteins comprising classical dynamins and related proteins are membrane remodelling agentsinvolved in several biological processes such as endocytosis, maintenance of organelle morphology and viralresistance. These large GTPases couple GTP hydrolysis with membrane alterations such as fission, fusion ortubulation by undergoing repeated cycles of self-assembly/disassembly. The functions of these proteins are regulatedby various post-translational modifications that affect their GTPase activity, multimerization or membrane association.Recently, several reports have demonstrated variety of such modifications providing a better understanding of themechanisms by which dynamin proteins influence cellular responses to physiological and environmental cues. In thisreview, we discuss major post-translational modifications along with their roles in the mechanism of dynaminfunctions and implications in various cellular processes.

    • Tetrahymena dynamin-related protein 6 self-assembles independent of membrane association

      USHA P KAR HIMANI DEY ABDUR RAHAMAN

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      Self-assembly on target membranes is one of the important properties of all dynamin family proteins. Drp6, a dynaminrelatedprotein in Tetrahymena, controls nuclear remodelling and undergoes cycles of assembly/disassembly on the nuclearenvelope. To elucidate the mechanism of Drp6 function, we have characterized its biochemical and biophysical propertiesusing size exclusion chromatography, chemical cross-linking and electron microscopy. The results demonstrate that Drp6readily forms high-molecular-weight self-assembled structures as determined by size exclusion chromatography andchemical cross-linking. Negative stain electron microscopy revealed that Drp6 assembles into rings and spirals at physiologicalionic strength. We have also shown that the recombinant Drp6 expressed in bacteria is catalytically active and itsGTPase activity is not enhanced by low salt. These results suggest that, in contrast to dynamins but similar to MxA, Drp6self-assembles in the absence of membrane templates, and its GTPase activity is not affected by ionic strength of the buffer.We discuss the self-assembly structure of Drp6 and explain the basis for lack of membrane-stimulated GTPase activity.

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