Mean-square hydrophobic moment for partially helical polypeptides

✍ Scribed by Maher M. Hamed; Wayne L. Mattice

• Publisher: Wiley (John Wiley & Sons)
• Year: 1984
• Tongue: English
• Weight: 639 KB
• Volume: 23
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360230204

✦ Synopsis

A mean-square helical hydrophobic moment, ( h 2 ) , is defined for polypeptides in analogy to the mean-square dipole moment, ( p 2 ) , for polymer chains. For a freely jointed polymer chain, ( p z ) is given by Zm:, where m, denotes the dipole moment associated with bond i. In the absence of any correlations in the hydrophobic moments of individual amino acid residues in the helix, ( h 2 ) is specified by ZHT, where H, denotes the hydrophobicity of residue i. The tendency for correlations in orientations of residue hydrophobic moments in helices therefore dictates the size of ( h 2 ) / ( H 2 ) , where ( H 2 ) denotes the average value of ZH; for all helices.

The value of ( h 2 ) / ( H 2 )

will be greater than one in amphiphilic helices. A necessary prerequisite for this diagnostic usage of ( h 2 ) / ( H 2 ) is that the residue hydrophobic moment be oriented perpendicular to the principal axis of the helix. Matrix-generation schemes are formulated that permit rapid evaluation of ( h 2 ) and ( H 2 ) . The behavior of ( h 2 ) / ( H 2 ) is illustrated by calculations performed for model sequential copolypeptides.