Electrostatic interactions helical model

Fig. 15. A single heptad repeat of an idealized model for coiled-coil proteins (Talbot and Hodges, 1982 Hodges et al., 1981). The primary driving force for formation of the structure arises from the interdigitation of the apolar leucyl side chains. In addition, electrostatic interactions between the oppositely charged residues on neighboring helices may also contribute to the stability of the parallel form of the coiled coil (Hodges et al., 1981).

N. K. Rogers and M. J. E. Sternberg,/. Mol. Biol., 174,527 (1984). Electrostatic Interactions in Globular Proteins. Different Dielectric Models Applied to the Packing of a-Helices. 

Figure 1. A. Primary structures of the c-Myc and Max LZs. Sequences are taken from Zervo a al. (26) and renumbered. B. Helical wheel diagram of the c-Myc-Max heterodimeric LZ. Potential interhelical electrostatic interactions have been discussed elsewhere (19,20). In the knobs-into-hole model (9), side-chains (knobs) at position <1 in the heptad repeat pack in the holes formed by consecutive g and a residues and two d positions. Accordingly, Max AsnSn is proposed to pack in the hole formed by Valid, Glu4g, GluSa and LeuSd on the c-Myc LZ. Similarly, Max Asnl9a is proposed to pack in the hole formed by LeulSd, ArglSg, Argl9a and Leu22d.

Considering these results, it may be concluded that the FeS-X domain with the two loops between helices Vlll and IX in PsaA and PsaB and the acidic surface residues on PsaC are crucial for the electrostatic interaction between the PsaC subunit and the PS-1 core complex. The relative position and orientation of the three PS-1 iron-sulfur clusters in the Kamlowski model in Fig. 12 (A) corresponds to the triangular arrangement established by X-ray crystallography " and embodies several features of the model ofRodday, Do, Chynwat, Frank and Biggins. ... 

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