Page 4 - U. Protein structure and function

[U. Protein structure and function-2]

Stringent starvation protein A, a novel ppGpp-binding

protein in E. coli

TANER DUYSAK¹, Che-Hun Jung¹

¹Molecular Medicine , Chonnam National University, Gwangju 61186, Korea

Stringent starvation protein A (SspA) is an RNA polymerase-associated protein and its expression is induced by
starvation for glucose, nitrogen, phosphate or amino acids or upon phage λ infection. SspA itself also serves as a
transcriptional regulator. SspA shows a sequence homology to glutathione S-transferases and the crystal structure

of SspA from Yersinia pestis reveals that SspA is structurally conserved to glutathione S-transferases. It is reported,

however, that SspA from various sources lacks glutathione S-transferase activity. The alarmone ppGpp, first reported
by Cashel and Gallant, serves as a master regulator not only for the bacterial response to stress but also for almost
all aspects of bacterial physiology, virulence, and immune evasion. In this study, SspA from Escherichia coli has been

cloned and overexpressed. Here we report that ppGpp binds to SspA. On the contrary to the previous reports, SspA
from Escherichia coli shows glutathione S-transferase activity. The binding affinity of ppGpp, GSH, 1-chloro-2,4-

dinitrobenzene to SspA was determined by fluorescence spectrometry, and the KD values for ppGpp, GSH and
CDNB were 109, 168 and 75 μM, respectively. The roles of ppGpp binding to the functions of SspA are under

investigation.