Sulfate-Binding Protein from Salmonella typhimurium : Physical Properties

Abstract

This protein binds sulfate strongly and is implicated in sulfate transport in Salmonella typhimurium. It has a molecular weight of 32,000 and an axial ratio of 4:1. Crystals are elongate prisms up to 0.5 millimeter. X-ray diffraction photographs give discrete crystalline reflections to a spacing of at least 2 angstroms. The unit cell is orthorhombic P2₁2₁2₁, with four molecules per unit cell of 40.8 by 47.5 by 136 angstroms. This is consistent with a highly asymmetric molecule such as the prolate ellipsoid suggested by the other physical measurements. Addition of sulfate had minimum effects on the physical properties as measured by light absorption, optical rotary dispersion, circular dichroism, fluorescence and its depolarization, nuclear magnetic resonance, and sedimentation velocity.