Thermodynamics Research Today is a free monthly online journal that collates and summarizes the latest research about Thermodynamics, including details on enthalpy, entropy, energy transitions.

Structural and thermodynamic encoding in the sequence of rat microsomal cytochrome b(5).

Lecomte JT, Mukhopadhyay K, Pond MP

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA. lecomte_jtj@jhu.edu

The water-soluble domain of rat microsomal cytochrome b(5) is a convenient protein with which to inspect the connection between amino acid sequence and thermodynamic properties. In the absence of its single heme cofactor, cytochrome b(5) contains a partially folded stretch of 30 residues. This region is recognized as prone to disorder by programs that analyze primary structures for such intrinsic features. The cytochrome was subjected to amino acid replacements in the folded core (I12A), in the portion that refolds only when in contact with the heme group (N57P), and in both (F35H/H39A/L46Y). Despite the difficulties associated with measuring thermodynamic quantities for the heme-bound species, it was possible to rationalize the energetic consequences of both types of replacements and test a simple equation relating apoprotein and holoprotein stability. In addition, a phenomenological relationship between the change in T(m) (the temperature at the midpoint of the thermal transition) and the change in thermodynamic stability determined by chemical denaturation was observed that could be used to extend the interpretation of incomplete holoprotein stability data. Structural information was obtained by nuclear magnetic resonance spectroscopy toward an atomic-level analysis of the effects.

Published 5 March 2008 in Biopolymers, 89(5): 428-42.
Full-text of this article is available online (may require subscription).

© 2005-2008 Thermodynamics Research Today. All Rights Reserved.