MHC-IIB Filament Assembly and Cellular Localization Are Governed by the Rod Net Charge

Actin-dependent myosin II molecular motors form an integral part of the cell cytoskeleton. Myosin II molecules contain a long coiled-coil rod that mediates filament assembly required for myosin II to exert its full activity. The exact mechanisms orchestrating filament assembly are not fully understood., negatively-charged regions of the coiled-coil were found to play an important role by controlling the intracellular localization of native MHC-IIB. The entire positively-charged region is also important for intracellular localization of native MHC-IIB.A correct distribution of positive and negative charges along myosin II rod is a necessary component in proper filament assembly and intracellular localization of MHC-IIB

Molecular basis of structure and function of the microvillus membrane of intestinal epithelial cells

Correlation of molecular structure with biochemical functions of the plasma membrane of the microvilli of intestinal epithelial cells has been investigated by biochemical and electron microscopic procedures. Repeating particles, measuring approximately 60 &#197;in diameter, were found on the surface of the microvilli membrane which had been isolated or purified from rabbit intestinal epithelial cells and negatively stained with phosphotungstic acid. These particles were proved to be inherent components of the microvillus membrane, attached to the outer surface of its trilaminar structure, and were designated as the elementary particles of the microvilli of intestinal epithelial cells. Biochemical and electron microscopic identification of these elementary particles has been carried out by isolation of the elementary particles with papain from the isolated microvillus membrane, followed by purification of the particles by chromatographies on DEAE-cellulose and Sephadex columns. The partially purified particles containing invertase and leucine aminopeptidase are similar in size and structure to those of the elementary particles in the microvillus membrane. Evidence indicates that each of the elementary particles coincide with or include an enzyme molecule such as disaccharidase or peptidase, which carry out the terminal hydrolytic digestion of carbohydrates and proteins, respectively, on the surface of the microvillus membrane. Magnesium ionactivated adenosine triphosphatase and alkaline phosphatase cannot be solubilized with papain but remains in the smooth-surface membrane after the elementary particles have been removed. Cytochemical electron microscopic observation revealed that the active site of magnesium ion-activated adenosine triphosphatase is localized predominantly in the inner surface of the trilaminar structure of the microvillus membrane.</p

Human complement activation by smooth and rough Proteus mirabilis lipopolysaccharides

Proteus mirabilis bacilli play an important role in human urinary tract infections, bacteremia, and rheumatoid arthritis. The authors previously studied human complement C3 conversion by smooth-form P. mirabilis O10, O23, O30, and O43 lipopolysaccharides (LPSs) and showed that smooth Proteus LPSs fragmented C3 in a dose- and time-dependent manner. In the present study, one smooth P. mirabilis S1959 and its two polysaccharide-truncated LPSs isolated from an R mutant strain were used to study the C3 conversion. The conversion of C3 to C3c by smooth and rough P. mirabilis LPSs was studied by capture ELISA and crossed immunoelectrophoresis. Proteins isolated from the outer membrane were analyzed by discontinuous sodium dodecyl sulfate gel electrophoresis. The smooth P. mirabilis S1959 (O3) strain was resistant to the bactericidal activity of human serum, in contrast to the Ra and Re mutant strains. The presence of an exposed core oligosaccharide in R110 LPS was not sufficient to protect the strain from serum-dependent killing. In addition to LPS structure, the outer-membrane proteins may also play roles in protecting the smooth P. mirabilis S1959 (O3) strain from the bactericidal action of serum. It was shown that the Ra P. mirabilis R110 and the Re P. mirabilis R45 mutants possess very different OMP compositions from that of the P. mirabilis S 1959 strain. Regardless of the complement resistance of the P. mirabilis strains, the S1959, R110, and R45 LPSs fragmented C3 and induced C3c neo-antigen exposure. The use of complement-deficient human serum allows the conclusion that the Re-type P. mirabilis R45 LPS fragmented C3 by the antibody-independent classical pathway