SHAPE AND ACCESSIBLE SURFACE-AREA OF GLOBULAR PROTEINS

The accessible surface area of a protein has been reported to be proportional to the 2 3 power of the real volume. When this relationship was compared to the area-volume relationship of simple geometric shapes, it was concluded that shape is not important in determining the accessible surface area and that spheres are good models for protein subunits. However, since the accessible surface area and the real volume are derived from different geometric figures, the relation between the two cannot be directly compared with the area-volume relationships of simple geometric shapes. When the volume of the geometric figure used to calculate the accessible surface area is estimated, the accessible area is proportional to the 0·77 power of that volume. Only this value can be directly compared with similar values for simple geometric figures. Indeed this comparison shows that protein molecules must be more aspherical at larger molecular weights, so shape is important in determining the area of a protein and spheres are not always good models for protein subunits. When the texture of the protein surface is considered, this comparison shows that protein molecules must be more aspherical or more textured at larger molecular weights. © 1979.