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. 1992 Aug 15;89(16):7315–7319. doi: 10.1073/pnas.89.16.7315

Role of loop-helix interactions in stabilizing four-helix bundle proteins.

K C Chou 1, G M Maggiora 1, H A Scheraga 1
PMCID: PMC49700  PMID: 1323830

Abstract

One of the critical issues regarding proteins with a four-helix bundle motif is which interactions play the major role in stabilizing this type of folded structure: the interaction among the four alpha-helices or the interaction between the loop and helix segments. To answer this question, an energetic analysis has been carried out for three proteins with a four-helix bundle--namely, methemerythrin, cytochrome b-562, and cytochrome c'. The structures on which the analysis has been made were derived from their respective crystallographic coordinates. All three proteins have long helices (16-26 residues) and most of their loops are short (3-5 residues). However, it was found in all three proteins that loop-helix interactions were stronger than helix-helix interactions. Moreover, not only the nonbonded component but also the electrostatic component of the interaction energy were dominated by loop-helix interactions rather than by interhelix interactions, although the latter involve favorable helix-dipole interactions due to the antiparallel arrangement of neighboring helices. The results of the energetic analysis indicate that the loop segments, whether they are in a theoretical model or in real proteins, play a significant role in stabilizing proteins with four-helix bundles.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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