Three-dimensional analysis of the 16 nm urothelial plaque particle: Luminal surface exposure, preferential head-to-head interaction, and hinge formation

The luminal surface of mouse urothelium in contact with the urine is almost entirely covered with plaques consisting of uroplakin-containing particles that form p6 hexagonal crystals with a center-to-center distance of 16 nm. A combination of quick-freeze/deep-etch images and our previous negative s taining data indicate that the head domain of the uroplakin particle, which is exposed without an extensive glycocalyx shield, interacts closely with the head domains of the neighboring particles, while the membrane-embedded tail domains are farther apart; and that urothelial particles and plaques a re not rigid structures as they can change their configuration in response to mechanical perturbations. Based on these data, we have constructed three -dimensional models depicting the structural organization of urothelial par ticles and plaques. Our models suggest that the head-to-head interaction ma y play a key role in determining the shape and size of the urothelial plaqu es. These models can explain many properties of urothelial plaques includin g their unique shape, detergent-insolubility, and morphological changes dur ing vesicle maturation. (C) 1999 Academic Press.