ISSN:
0886-1544
Keywords:
α-helix
;
filament motility
;
filament contractility
;
filament sliding
;
microtubules
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
The twisting behavior of α helices has hardly been considered hitherto with regard to the function of proteins. The well-known electrostatic repulsion between the highly charged side chains, which depends on their interaction with ions, is absolutely connected with torsional rotations of the helix as long as its hydrogen bonds hold. This means a direct transformation of chemical into mechanical energy. However, the stability of a twisted single α helix with charged side chains is low in an aqueous environment. It may easily ball up to form a globular molecule with nonhelical regions of the polypeptide chain. This corresponds to a primitive contraction that obviously occurs with spasminlike proteins that contain strongly twisted filaments as Salisbury [J. Submicrosc. Cytol. 15:105-110, 1983] has shown. Steps that increase the stability and rigidity of α helical filaments are (1) the formation of coiled-coils, (2) self-intertwining (“telephone cord phenomenon”) or intertwining with other coiled-coils as shown with the intermediate filaments, and (3) association with cytoskeletal elements (microfilaments, protofilaments of microtubules) that contain globular subunits. These coarser elements are rotated by winding and unwinding of the smaller helical molecules and thus transmit the torsion produced in the α helices to the microscopic level by the sliding (screwing) motion and the shearing effect that is connected with the waves of a rotating helix. Particles are transported if connected to the helical side arms. Since the displacement of the side arms seems to occur along the single protofilaments of a microtubule, a rotation of these protofiiaments is suggested. The bidirectional transport of particles along single microtubules may be explained by the association of left- and right-handed helices with the protofilaments. According to the models, parallel and antiparallel sliding of neurofilaments and neurotubules is suggested.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cm.970060223
