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Volume 8
Journal of Biotechnology & Biomaterials
ISSN: 2155-952X
Biotech Congress 2018 & Enzymology 2018
March 05-07, 2018
Page 36
conference
series
.com
JOINT EVENT
20
th
Global Congress on
Biotechnology
3
rd
International Conference on
Enzymology and Molecular Biology
&
March 05-07, 2018 London, UK
Peter J F Henderson, J Biotechnol Biomater 2018, Volume 8
DOI: 10.4172/2155-952X-C2-090
Kinetic and molecular dissection of coupled ion-substrate membrane transport proteins
T
he Mhp1 Na
+
, -hydantoin membrane symport protein from
Microbacterium liquefaciens
is a paradigm for the nucleobase-
cation-symport, NCS-1, family of transport proteins found widely in archaebacteria, bacteria, yeasts and plants. Their
metabolic roles include the capture by cells of nitrogen compounds and vitamins from the environment. Mhp1 is also a
structural model for the huge range of ‘5-helix-inverted-repeat’ superfamily of proteins, because, unusually, crystal structures
are available for its open-outwards, occluded, and open-inward conformations. Here we accomplish a detailed dynamic model
of the partial reactions in an alternating access cycle of membrane transport derived from substrate binding studies to the
purified Mhp1 protein by combining novel mass spectrometry, stopped-flow and steady state kinetic analyses and mutagenesis.
The mechanism of coupling substrate transport to the Na
+
, -gradient is revealed during a sequence of mostly reversible kinetic
steps that explain how transfer of substrate across the membrane is affected by changes in conformational states. The AceI
H
+
/substrate antiport protein from Acinetobacter baumannii is a paradigm for the proteobacterial antimicrobial compound
efflux (PACE) family of drug efflux proteins found dispersed throughout the Proteobacteria. AceI contributes to the resistance
of Acinetobacter baumannii towards the widely used antiseptic, chlorhexidine. Currently there is little structural information
about the PACE family of transport proteins, but progress towards understanding the recognition of substrates and cations by
AceI and its homologues will be discussed.
Figure 1
: Scheme for the coupled transport of Na+ and hydantoins by Mhp1.
Recent Publications
1. Shimamura T, Weyand S, Beckstein O, Rutherford N G, Hadden J M et al. (2010) Molecular basis of alternating access
membrane transport by the sodium-hydantoin transporter Mhp1. Science. 328(5977):470-473.
2. Simmons K J, Jackson S M, Brueckner F, Patching S G, Beckstein O et al. (2014) Molecular mechanism of ligand
recognition by membrane transport protein. Mhp1. EMBO J. 33(16):1831-1944.
3. Calabrese A N, Jackson S M, Jones L N, Beckstein O, Gsponer J (2017) Topological dissection of the membrane
Peter J F Henderson
1
Astbury Centre for Structural Molecular Biology - University of Leeds, UK
2
Macquarie University, Australia