Phosphorus-31 nuclear magnetic resonance study of internal motion in ribonucleic acid of southern bean mosaic virus.

Abstract

Phosphorus-31 nuclear magnetic resonance spectroscopy was used to study southern bean mosaic virus (SBMV) in its native and ethylenediaminetetraacetic acid treated forms at various pH values in the range 4.5-9.0. The degree of swelling in the latter form is a critical function of pH. Spin-lattice relaxation time (T1), line-width, and nuclear Overhauser effect (NOE) measurements were made at 40.51, 80.98, and 190.3 MHz. The results indicate that the RNA phosphate groups in native SBMV exhibit low-amplitude internal motions on a nanosecond time scale while the phosphate groups of swollen virus exhibit large-amplitude, more rapid, internal motions. A spread of T1 and NOE values is measured at intermediate stages in the swelling process. A simple explanation, consistent with the data, is that the RNA core of the virus undergoes a two-state phase transition from a relatively rigid, compact solid form in the native SBMV to a mobile, solvated state in the fully swollen particle.