Human health is closely related to the structure and function of a protein. Generally, the hierarchy of protein structure can be divided into primary, secondary, tertiary and quaternary structures in the textbook. However, there are also the quinary interactions, which can drive macromolecules to form a “inherently transient” complex, described as the “quinary structure”, as for proteins jam-packed in a cell environment (also known as in vivo). Researchers are always wondering if the quinary interactions may change some functions of proteins in cell. That is to say, the biophysical properties of proteins in vivo might be different from those in vitro (studies performed with microorganisms, cells, or biological molecules outside their normal biological context). However, the research about the quinary interactions is sparse, because currently it is difficult to detect such kind of weak and short-lived interactions.  

The Modelling and Simulation Group, led by Professor YAO Lishan from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy Sciences, studied the quinary interactions of proteins in the cell-like environment (Lysate) by using a remote chemical shift perturbations (CSPs) method (J. Am. Chem. Soc., 2014, 136: 12816), also developed by this group. 

The results indicated that the quinary interactions indeed weaken the electric field generated by protein side-chain charges in the cell-like environment (Figure 1), but with no effect on the protein backbone structure. Furthermore, it was also found that the electrical field weakening is related with the location and sign (+/-) of the charged side-chain. It can therefore be expected that, the quinary interaction can be reasonably adjusted by charge redistribution.  

This study was recently published on Journal of the American Chemical Society. The result may also permit one to predict these interactions for any protein with a known structure. Note that this research was conducted in a cell-like environment, a state very close to the real physiological state. The in vivo study on the quinary interactions is now under way in this group. 

Figure 1. Quinary interactions weaken electrical field (E-field) generated by protein side-chain charges in the cell-like environment (Image by QIBEBT).

Reference: 

Quinary Interactions Weaken the Electric Field Generated by Protein Side Chain Charges in the Cell-like Environment, Journal of the American Chemical Society, 2017, 139 (2): 647. 

Contact: Prof. YAO Lishan 

Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences 

Email: yaols@qibebt.ac.cn