Coronavirus Pleomorphism and Rotational Diffusivity

The coronavirus is always idealized as a spherical capsid with radially protruding spikes. However, histologically, in the tissues of infected patients, capsids in cross section are elliptical, and only sometimes spherical. This capsid ellipticity implies that coronaviruses are oblate or prolate or both. We call this diversity of shapes, pleomorphism. Recently, the rotational diffusivity of the coronavirus in suspension was calculated, from first principles, using general rigid bead-rod theory [M.A. Kanso, Phys Fluids, 32, 113101 (2020)]. We did so by beading the capsid, and then also by replacing each of its bulbous spikes with a single bead. We use energy minimization for the spreading of the spikes, charged identically, over the oblate or prolate capsids. We use general rigid bead-rod theory to explore the role of coronavirus ellipticity on its rotational diffusivity, the transport property around which its cell attachment revolves. We learn that coronavirus ellipticity decreases its rotational diffusivity for both oblate and prolate ellipsoids.