# Structural consequences of replacement of an \alpha-helical Pro residue in Escherichia coli thioredoxin

Rudresh, * and Jain, Rinku and Dani, Vardhan and Mitra, Ashima and Srivastava, Sarika and Sarma, Siddhartha P and Varadarajan, R and Ramakumar, S (2002) Structural consequences of replacement of an \alpha-helical Pro residue in Escherichia coli thioredoxin. In: Protein Engineering, 15 (8). pp. 627-633.

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## Abstract

While it is well known that introduction of Pro residues into the interior of protein $\alpha$-helices is destabilizing, there have been few studies that have examined the structural and thermodynamic effects of the replacement of a Pro residue in the interior of a protein $\alpha$-helix. We have previously reported an increase in stability in the P40S mutant of Escherichia coli thioredoxin of 1–1.5 kcal/mol in the temperature range 280–330 K. This paper describes the structure of the P40S mutant at a resolution of 1.8 \AA. In wild-type thioredoxin, P40 is located in the interior of helix two, a long $\alpha$-helix that extends from residues 32 to 49 with a kink at residue 40. Structural differences between the wild-type and P40S are largely localized to the above helix. In the P40S mutant, there is an expected additional hydrogen bond formed between the amide of S40 and the carbonyl of residue K36 and also additional hydrogen bonds between the side chain of S40 and the carbonyl of K36. The helix remains kinked. In the wild-type, main chain hydrogen bonds exist between the amide of 44 and carbonyl of 40 and between the amide of 43 and carbonyl of 39. However, these are absent in P40S. Instead, these main chain atoms are hydrogen bonded to water molecules. The increased stability of P40S is likely to be due to the net increase in the number of hydrogen bonds in helix two of E.coli thioredoxin.

Item Type: Journal Article Copyright belongs to this articles is Oxford University Press. α-helix;Mutant;Proline;Thermal stability;Thioredoxin Division of Biological Sciences > Molecular Biophysics UnitDivision of Information Sciences > BioInformatics CentreDivision of Physical & Mathematical Sciences > Physics 16 Oct 2007 19 Sep 2010 04:40 http://eprints.iisc.ernet.in/id/eprint/12296