[Cytoadherence in cerebral malaria as particular example of pathology in host--parasite system]. / Cytoadherencja w malarii mózgowej jako szczególny przyklad patologii w ukladzie gospodarz--pasozyt.

Cerebral malaria in man and in animals is the consequence of a cascade of events, involving the patological changes, leading to the amplification of the expression of the receptors for cytoadherence on brain capillary endothelial cells. Sequestration is the process by which erytrocytes infected with the mature forms of the malaria parasite Plasmodium falciparum disappear from circulation and accumulate within venules and capillaries of various organs and tissues. The molecular mechanism in sequestration is one of the most rapidly advancing fields in malaria research. The several specific aspects considered in this paper. Our electron micrographs show cytoadherence in own model of cerebral malaria in rats infected with Plasmodium berghei.

A beta turn in the cytoplasmic tail of the integrin alpha v subunit influences conformation and ligand binding of alpha v beta 3.

Integrins undergo conformational alterations in response to extracellular or intracellular stimuli, suggesting that structural elements within their exo- and cytoplasmic domains cooperate during transmembrane signaling. In this report, we identify a beta turn in the cytoplasmic tail of the alpha v subunit that impacts the ligand binding and conformation of the alpha v beta 3 heterodimer. Cells expressing a mutant alpha v beta 3 heterodimer composed of a truncated alpha v subunit, alpha v1000, lacking 18 carboxyl-terminal amino acids exhibits wild-type receptor structure and function. However, a truncation mutant, alpha v995, lacking five additional residues (PPQEE), which define a beta turn, is deficient in vitronectin and fibrinogen adhesion. This alteration in adhesive function is associated with two detectable structural changes in the alpha v beta 3 heterodimer. First, the alpha v995 membrane-spanning light chain exhibits retarded electrophoretic mobility on SDS-polyacrylamide gels. Second, the alpha v995 beta 3 receptor shows an altered chymotryptic profile as measured by the loss of a 39-kDa proteolytic fragment from its ectodomain. These findings demonstrate that the ligand binding and structural properties of the intact alpha v beta 3 heterodimer can be influenced by a beta turn within the cytoplasmic tail of its alpha v subunit. The presence of homologous beta turns within other alpha subunit cytoplasmic tails suggests that this structural motif may play a role in regulating integrin-mediated bidirectional transmembrane signals.

Pattern formation and handedness in the cytoskeleton of human platelets.

The cytoskeletal patterns of human platelets spread on a glass surface are analyzed. F-actin is arranged in patterns of parallel microfilaments, microfilaments forming triangles, or microfilaments radiating tangentially from a central ellipse or circle. Vinculin, a cytoskeletal protein, is located at both ends of the filaments. In platelets with tangentially radiating microfilaments, vinculin patches are aligned on the branches of a two-armed spiral. The spirals are always left-handed. Talin and two integrins (gpIIb-IIIa, vitronectin receptor), proteins usually associated with focal contacts in tissue culture cells, are not concentrated at the ends of microfilaments in human platelets. It is suggested that the distribution of vinculin is due to competitive aggregation of vinculin close to the inner leaflet of the ventral plasma membrane and that sites of cytoskeleton-membrane linkage are important for generating supramolecular asymmetries of biological systems.