15N NMR relaxation and H/D exchange experiments revealed that binding of dT 7 increases the stability of Bs-CspB and reduces the sub-nanosecond dynamics of the entire protein and especially of loop β3–β4.Ī rapid reduction in growth temperature induces the cold shock response of many prokaryotic organisms by down-regulation of the expression of most proteins ( 1) and transient up-regulation of a small set of proteins ( 2, 3). A variation of the ssDNA affinity is accomplished solely by changes of the dissociation rate. Binding studies of protein variants and mutated ssDNA demonstrated that Bs-CspB associates with ssDNA at almost diffusion controlled rates and low sequence specificity consistent with its biological function. Bs-CspB reveals an almost invariant conformation when bound to dT 7 with only minor reorientations in loop β1–β2 and β3–β4 and of few aromatic side chains involved in base stacking. We determined the solution structure of Bs-CspB bound to the single-stranded DNA (ssDNA) fragment heptathymidine (dT 7) by NMR spectroscopy. CSP are believed to function as ‘RNA chaperones’ and during anti-termination. Cold shock proteins (CSP) belong to the family of single-stranded nucleic acid binding proteins with OB-fold.
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