Affiliation:
1. Institute of Microbial Technology, Chandigarh-160014, India
Abstract
ABSTRACT
In the strictly aerobic, gram-negative bacterium
Vitreoscilla
strain C1, oxygen-limited growth conditions create a more than 50-fold increase in the expression of a homodimeric heme protein which was recognized as the first bacterial hemoglobin (Hb). The recently determined crystal structure of
Vitreoscilla
Hb has indicated that the heme pocket of microbial globins differs from that of eukaryotic Hbs. In an attempt to understand the diverse functions of Hb-like proteins in prokaryotes, we have cloned and characterized the gene (
vgb
) encoding an Hb-like protein from another strain of
Vitreoscilla
,
V. stercoraria
DW. Several silent changes were observed within the coding region of the
V. stercoraria vgb
gene. Apart from that,
V. stercoraria
Hb exhibited interesting differences between the A and E helices. Compared to its Hb counterpart from
Vitreoscilla
strain C1, the purified preparation of
V. stercoraria
Hb displays a slower autooxidation rate. The differences between
Vitreoscilla
Hb and
V. stercoraria
Hb were mapped onto the three-dimensional structure of
Vitreoscilla
Hb, which indicated that the four changes, namely, Ile7Val, Ile9Thr, Ile10Ser, and Leu62Val, present within the
V. stercoraria
Hb fall in the region where the A and E helices contact each other. Therefore, alteration in the relative orientation of the A and E helices and the corresponding conformational change in the heme binding pocket of
V. stercoraria
Hb can be correlated to its slower autooxidation rate. In sharp contrast to the oxygen-regulated biosynthesis of Hb in
Vitreoscilla
strain C1, production of Hb in
V. stercoraria
has been found to be low and independent of oxygen control, which is supported by the absence of a fumarate and nitrate reductase regulator box within the
V. stercoraria vgb
promoter region. Thus, the regulation mechanisms of the Hb-encoding gene appear to be quite different in the two closely related species of
Vitreoscilla
. The relatively slower autooxidation rate of
V. stercoraria
Hb, lack of oxygen sensitivity, and constitutive production of Hb suggest that it may have some other function(s) in the cellular physiology of
V. stercoraria
DW, together with facilitated oxygen transport, predicted for earlier reported
Vitreoscilla
Hb.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
14 articles.
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