>On 12 May 1997, Weiping Jiang wrote:
>>> Hi, there:
>>>> In the standard alpha helix, every amino acid residue turns 100 degrees to
>> form a helix. How about proline? It could turn more (>100 degrees) or just
>> bends the helix? Any comments are welcome!
>>>> Weiping
>>>On 12 May 1997, G.N replied:
>> Dear Weiping:
>> If you can read anything except e-mail, please read any textbook
> on protein chemistry/biophysics and NOT WASTE OUR TIME.
>> Hope it helps.
>
Much too harsh. The question is not found in most texbooks, if present at
all. The effect of the Pro in introducing a kink in the alpha-helix is well
documented. However, the kink is normally described as a bend, while there
is a concomitant twisting of the helix faces introduced by the Pro. Because
the kink region, comprising one turn before the pro residue, does not
necessarily have a 3.6 residues per turn periodicity as found for
a-helices, then a Pro-kink would shift out of register the periodicity of
the a-helix fragment before and the a-helix fragment after the pro-kink; we
refer to this effect as "face-twist". This "face-twisting" was first
reported in 1992 by us and another laboratory (Ballesteros, J. A., and
Weinstein, H. (1992) Biophys J 62(1), 107-9
; Sankararamakrishnan, R., and Vishveshwara, S. (1992) Int J Pept Protein
Res 39(4), 356-63).You can find a review of this subject in our chapter on
modeling GPCRs (Ballesteros, J. A., and Weinstein, H. (1995) Methods
Neurosci. 25, 366-428). We have also show how the "face-twisting" effect of
a Pro-kink could explain the accessibility pattern found for transmembrane
helix seven of the D2 receptor using the substituted cysteine accessibility
method (Fu, D., Ballesteros, J. A., Weinstein, H., Chen, J., and Javitch,
J. A. (1996) Biochemistry 35(35), 11278-85).
Juan Ballesteros.
______________________________________
Juan A. Ballesteros
Dept. Physiology & Biophysics
Box 1218
Mount Sinai School of medicine
New York, N.Y. 10029, U.S.A.
Tel: 1-212-241-6842
Fax: 1-212-860-3369
