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- Computer models of a new deoxy-sickle cell hemoglobin fiber ...Computer models of a new deoxy-sickle cell hemoglobin fiber based on x-ray diffraction data
Biophysical Journal, Volume 61, Issue 6, 1 June 1992, Pages 1638-1646
X.Q. Mu and B.M. Fairchild
AbstractA new x-ray fiber diffraction pattern from deoxygenated sickle cell erythrocytes has been observed. It displays 14 layer lines with a 109 A periodicity compared with the 64 A periodicity of the "classic" sickle cell hemoglobin (HbS) fiber. These data and association energy calculations serve as a basis for computer model building. Systematic searches over four-dimensional parameter space yielded twelve protofilament models that satisfy the following constraints: (a) two HbS molecules be related by twofold screw symmetry with a translational repeat of 109 A; (b) at least one of the substituted residues in HbS, val beta 6, should participate in intermolecular contacts; and (c) the energy of intermolecular interaction be less than -24 kcal/mol. Each of the protofilament models is a zigzag mono-strand that stands in contrast to the double-stranded protofilament of the "classic" fiber. Fiber models were constructed with each of the 12 protofilament models, pseudo-hexagonally packed. Searches of variable packing parameters showed four fiber models with minimal protofilament association energies and minimal differences between calculated transforms and observed data. The R-factor was less than 0.24 for each of these four models. In three of the fiber models the protofilament association energy is between -(93 and 130) kcal, and in a fourth, the energy is -64 kcal. One protofilament model constituted three distinct fiber models of the lower energy class, and a second protofilament model packed with a higher association energy into a fourth fiber model. The selection of a unique fiber model from among these four cannot be made because of the limited available data.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract | PDF (1023 kb) - Calculation of a Gap Restoration in the Membrane Skeleton of...Calculation of a Gap Restoration in the Membrane Skeleton of the Red Blood Cell: Possible Role for Myosin II in Local Repair
Biophysical Journal, Volume 76, Issue 3, 1 March 1999, Pages 1153-1165
C. Cibert, G. Prulière, C. Lacombe, C. Deprette and R. Cassoly
AbstractHuman red blood cells contain all of the elements involved in the formation of nonmuscle actomyosin II complexes (V. M. Fowler. 1986. 31:1–9; 1996. 8:86–96). No clear function has yet been attributed to these complexes. Using a mathematical model for the structure of the red blood cell spectrin skeleton (M. J. Saxton. 1992. 155:517–536), we have explored a possible role for myosin II bipolar minifilaments in the restoration of the membrane skeleton, which may be locally damaged by major mechanical or chemical stress. We propose that the establishment of stable links between distant antiparallel actin protofilaments after a local myosin II activation may initiate the repair of the disrupted area. We show that it is possible to define conditions in which the calculated number of myosin II minifilaments bound to actin protofilaments is consistent with the estimated number of myosin II minifilaments present in the red blood cells. A clear restoration effect can be observed when more than 50% of the spectrin polymers of a defined area are disrupted. It corresponds to a significant increase in the spectrin density in the protein free region of the membrane. This may be involved in a more complex repair process of the red blood cell membrane, which includes the vesiculation of the bilayer and the compaction of the disassembled spectrin network.
Abstract | Full Text | PDF (752 kb) - Mitosis: Riding the Protofilament CurlMitosis: Riding the Protofilament Curl
Current Biology, Volume 16, Issue 6, 21 March 2006, Pages R214-R216
Lynne Cassimeris
SummaryMore than 50 years ago, microtubule depolymerization was proposed as the force responsible for chromosome movement. New studies measure the force produced by depolymerization and show that protein ring complexes can couple depolymerization to movement. These results have implications for anaphase chromosome motility and mitotic evolution.
Summary | Full Text | PDF (74 kb) - …more
Copyright © 1980 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 32, Issue 1, 347-360, 1 October 1980
doi:10.1016/S0006-3495(80)84961-7
Research Article
Patterns in the quinary structures of proteins. Plasticity and inequivalence of individual molecules in helical arrays of sickle cell hemoglobin and tubulin
S.J. Edelstein
Abstract
The four recognized levels of organization of protein structure (primary through quaternary) are extended to add the designation quinary structure for the interactions within helical arrays, such as found for sickle cell hemoglobin fibers or tubulin units in microtubules. For sickle cell hemoglobin the main quinary structure is a 14-filament fiber, with a number of other minor forms also encountered. Degenerate forms of the 14-filament fibers can be characterized that lack specific pairs of filaments; evidence is presented which suggests an overall organization of the 14 filaments in pairs, with particular pairs aligned in an antiparallel orientation. For tubulin, a range of quinary structures can be detected depending on the number of protofilaments and whether adjacent protofilaments composed of alternating alpha- and beta-subunits are aligned with contacts between like or unlike subunits and with parallel or antiparallel polarity. Thus, in contrast to quarternary structure, which generally involves a fixed number of subunits, the quinary structures of proteins can exhibit marked plasticity and inequivalence in the juxtaposition of constituent molecules.
