Structural studies of human serum albumin using cryo-EM up to 0.38 nm resolution.

Abstract

Single particle cryo-electron microscopy (cryoEM) offers for large proteins the resolution close to the crystallographic resolution. Unfortunately, the current limitation for cryoEM is the molecular weight, and the smallest proteins, tested individually by the cryoEM method, rarely are less than 100 kDa in size. The aim of our research was to study the structure of human serum albumin and its oligomeric forms using a combination of cryoEM, small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). HSA is a monomeric (66.4 kDa) protein, which for years has been a model system for the transport of drugs and other substances, because in the human body it binds and carries lipids or metal cations (including zinc and copper ions) as well as for basic biophysical research. Currently, over 130 HSA structures in complexes with various ligands and alone at the resolution ranging from 0.189 nm to 0.39 nm have been deposited in Protein Data Bank. Using cryoEM, we were able to obtain the HSA structure with a 0.38 nm resolution. At present, it is probably one of the smallest protein structures determined using cryoEM at near-crystallographic resolution. Using SAXS and DLS we analyzed the HSA monomer structure and its oligomers in solution and compared with the cryoEM model. This research was funded by National Science Centre (Poland), grant number 2017/27/B/ST4/00485.