PEG-protein interaction induced contraction of NalD chains

Jiyan Yu; Weizhong Chen; Chi Wu; Hao Chen

doi:10.1371/journal.pone.0096616

PEG-protein interaction induced contraction of NalD chains

PLoS One. 2014 May 8;9(5):e96616. doi: 10.1371/journal.pone.0096616. eCollection 2014.

Authors

Jiyan Yu¹, Weizhong Chen¹, Chi Wu², Hao Chen³

Affiliations

¹ Department of Chemical Physics, University of Science and Technology of China, Hefei, China; Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China.
² Department of Chemical Physics, University of Science and Technology of China, Hefei, China; Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, China.
³ Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China.

Abstract

In a recent attempt to crystallize a regulator of MexAB-OprM multi-drug efflux systems in Pseudomonas aeruginosa (NalD), we found that adding polyethylene glycol (PEG3350, Mw = 3,350 g/mol) into the protein solution increases the speed of NalD migration in gel electrophoresis, signaling a smaller hydrodynamic size. At first we conjectured that NalD was degraded unexpectedly by PEG; however, we found that there was no change in its molar mass by MALDI-TOF characterization. Moreover, we found that adding polyacrylic acid (PAA) into the solution mixture returned the NalD migration to its normal speed. Furthermore, our analytic ultracentrifugation and dynamic laser light scattering results directly reveal that NalD interacts with PEG so that individual NalD chains gradually shrink as more PEG chains are added in the range of 10-50 mg/mL. Size exclusion chromatography also confirms that the NalD chain shrinks in the presence of PEG. A combination of these results indicates that PEG3350 chains can complex with NalD to induce an intra-protein chain contraction, presumably via the formation of hydrogen bond between -C-O-C- on PEG and -COOH on NalD, resulting in a smaller hydrodynamic size (faster migration) and a higher apparent molar mass. Note that because the presence of PEG affects osmotic pressure, it is considered to be a precipitator of protein crystallization. Our current finding reveals that the interaction of PEG/protein may play a significant role in protein crystallization. The complexation potentially makes the protein chain segments less flexible, and consequently makes crystallization easier. Hopefully, our current results will stimulate further studies in this direction.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bacterial Proteins / chemistry*
Bacterial Proteins / metabolism*
Dose-Response Relationship, Drug
Hydrodynamics
Models, Molecular
Polyethylene Glycols / metabolism*
Polyethylene Glycols / pharmacology*
Protein Binding
Protein Conformation / drug effects
Pseudomonas aeruginosa*

Substances

Bacterial Proteins
Polyethylene Glycols

Grants and funding

The financial support of the National Natural Science Foundation of China (21071077 and 91013009, http://www.nsfc.gov.cn/), the New Teachers’ Fund for Doctor Stations, Ministry of Education of China (20100091120029, http://www.moe.edu.cn/), the Fundamental Research Funds for the Central Universities (1095020516 and 1116020501, http://www.moe.edu.cn/), the Ministry of Science and Technology of China Key Project (2012CB933802, http://www.most.gov.cn/), and the Hong Kong Special Administration Region Earmarked Projects (CUHK4042/10P, 2130241; 2060405; and CUHK4036/11P, 2130281; 2060431, http://www.ugc.edu.hk/eng/rgc/index.htm) is gratefully acknowledged. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.