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J. Bacteriol., 05 1995, 2644-2653, Vol 177, No. 10
LD Cope, R Yogev, U Muller-Eberhard and EJ Hansen
The utilization of heme bound to the serum glycoprotein hemopexin by
Haemophilus influenzae type b (Hib) strain DL42 requires the presence of
the 100-kDa heme:hemopexin-binding protein encoded by the hxuA gene (M. S.
Hanson, S. E. Pelzel, J. Latimer, U. Muller-Eberhard, and E. J. Hansen,
Proc. Natl. Acad. Sci. USA 89:1973-1977, 1992). Nucleotide sequence
analysis of a 5-kb region immediately upstream from the hxuA gene revealed
the presence of two genes, designated hxuC and hxuB, which encoded outer
membrane proteins. The 78-kDa HxuC protein had similarity to TonB-dependent
outer membrane proteins of other organisms, whereas the 60-kDa HxuB
molecule most closely resembled the ShlB protein of Serratia marcescens. A
set of three isogenic Hib mutants with cat cartridges inserted individually
into their hxuA, hxuB, and hxuC genes was constructed. None of these
mutants could utilize heme:hemopexin. The hxuC mutant was also unable to
utilize low levels of free heme, whereas both the hxuA and hxuB mutants
could utilize free heme. When the wild-type hxuC gene was present in trans,
the hxuC mutant regained its ability to utilize low levels of free heme but
still could not utilize heme:hemopexin. The hxuA mutant could utilize
heme:hemopexin when a functional hxuA gene from a nontypeable H. influenzae
strain was present in trans. Complementation analysis using this cloned
nontypeable H. influenzae hxuA gene also indicated that the HxuB protein
likely functions in the release of soluble HxuA from the Hib cell.(ABSTRACT
TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
A gene cluster involved in the utilization of both free heme and heme:hemopexin by Haemophilus influenzae type b
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
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