Abstract. The isolated membrane skeleton of human erythrocytes was studied by high resolution negative staining electron microscopy. When the skeletal meshwork is spread onto a thin carbon film, clear images of a primarily hexagonal lattice of junctional F-actin complexes crosslinked by spectrin filaments are obtained. The regularly ordered network extends over the entire membrane skeleton. Some of the junctional complexes are arranged in the form of pentagons and septagons, •3 and 8 %, respectively. At least five forms of spectrin crosslinks are detected in the spread skeleton including (a) a single spectrin tetramer linking two junctional complexes, (b) three-armed Y-shaped spectrin molecules linking three junctional complexes, (c) three-armed spectrin molecules connecting two junctional complexes with two arms bound to one complex and the third arm bound to the adjacent complex, (d) double spectrin filaments linking two junctional complexes, and (e) four-armed spectrin molecules linking two junctional complexes. Of these, the crosslinks of single spectrin tetramers and three-armed molecules are the most abundant and represent 84 and 11% of the total crosslinks, respectively. These observations are compatible with the presence of spectrin tetramers and oligomers in the erythrocyte membrane skeleton. Globular structures (9-12 nm in diameter) are attached to the majority of the spectrin tetramers or higher order oligomer-like molecules, "080 nm from the distal ends of the spectrin tetramers. These globular structures are ankyrinor ankyrin/band 3-containing complexes, since they are absent when ankyrin and residual band 3 are extracted from the skeleton under hypertonic conditions.

The red blood cell (RBC) membrane protein AE1 provides high affinity binding sites for the membrane skeleton, a structure critical to RBC integrity. AE1 biosynthesis is postulated to be required for terminal erythropoiesis and membrane skeleton assembly. We used targeted mutagenesis to assess AE1 function in vivo. RBCs lacking AE1 spontaneously shed membrane vesicles and tubules, leading to severe spherocytosis and hemolysis, but the levels of the major skeleton components, the synthesis of spectrin in mutant erythroblasts, and skeletal architecture are normal or nearly normal. The results indicate that AE1 does not regulate RBC membrane skeleton assembly in vivo but is essential for membrane stability. We postulate that stabilization is achieved through AE1-lipid interactions and that loss of these interactions is a key pathogenic event in hereditary spherocytosis.

We report the molecular identification of a sialic acid-independent host–parasite interaction in the Plasmodium falciparum malaria parasite invasion of RBCs. Two nonglycosylated exofacial regions of human band 3 in the RBC membrane were identified as a crucial host receptor binding the C-terminal processing products of merozoite surface protein 1 (MSP1). Peptides derived from the receptor region of band 3 inhibited the invasion of RBCs by P. falciparum. A major segment of the band 3 receptor (5ABC) bound to native MSP142 and blocked the interaction of native MSP142 with intact RBCs in vitro. Recombinant MSP119 (the C-terminal domain of MSP142) bound to 5ABC as well as RBCs. The binding of both native MSP142 and recombinant MSP119 was not affected by the neuraminidase treatment of RBCs, but sensitive to chymotrypsin treatment. In addition, recombinant MSP138 showed similar interactions with the band 3 receptor and RBCs, although the interaction was relatively weak. These findings suggest that the chymotrypsin-sensitive MSP1–band 3 interaction plays a role in a sialic acid-independent invasion pathway and reveal the function of MSP1 in the Plasmodium invasion of RBCs

Southeast Asian ovalocytosis (SAO) is a hereditary condition that is widespread in parts ofSoutheast Asia.