Extensive cross-linking of calf brain plain synaptic vesicle proteins

Calf brain plain synaptic vesicle proteins have been cross-linked with bis[2-(succinimidooxycarbonyloxy)ethyl] sulfone, a homobifunctional, cleavable reagent, as well as with N-hydroxysuccinimidyl 4-azidobenzoate, a photosensitive, heterobifunctional reagent. These results demonstrate the generality of a recent report that synaptic vesicle proteins can be cross-linked, in contrast to a prior report that no cross-linking could be observed. The reagents gave some differences in the proteins that were preferentially cross-linked. A protein at Mr = 173 000, which comigrates with clathrin, is present in the plain synaptic vesicle fraction and appears to be involved in cross-linking. A high degree of association and structural organization of synaptic vesicle proteins is suspected, since extensive cross-linking of most synaptic vesicle proteins with high-molecular-mass proteins, which are probably structural in nature, is observed. A protein with an Mr of 249 000 is specifically cross-linked to a protein of Mr 42 000, probably actin, suggesting that the 249 000-Mr protein may be a spectrin-like molecule. The present results suggest that synaptic vesicles may be organized by a spectrin-like matrix similar to that observed in erythrocytes and other cells.