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Lipoprotein biogenesis in Pseudomonas aeruginosa: characterisation of the periplasmic chaperone LolA

Wednesday, 10 November, 2010 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
Faculty: Science and Bio-engineering Sciences
Kim Remans
phd defence

Many lipoproteins reside in the outer membrane of Gram-negative bacteria, and their
biogenesis is dependent on the Lol (localization of lipoproteins) system. The periplasmic
chaperone LolA accepts outer membrane-destined lipoproteins that are released from the
inner membrane by the LolCDE complex and transfers them to the outer membrane
receptor LolB. The exact nature of the LolA–lipoprotein complex is still unknown. The
crystal structure of Escherichia coli LolA features an open β-barrel covered by α-helices
that together constitute a hydrophobic cavity, which would allow the binding of one acyl
chain. However, outer membrane lipoproteins contain three acyl chains, and the
stoichiometry of the LolA–lipoprotein complex is 1:1. Here we present the crystal
structure of Pseudomonas aeruginosa LolA that projects clear hydrophobic surface
patches. Since these patches are large enough to accommodate acyl chains, their role in
lipoprotein binding was investigated. Several LolA mutant proteins were created, and
their functionality was assessed by studying their capacity to release lipoproteins
produced in sphaeroplasts. Interruption of the largest hydrophobic patch completely
destroyed the lipoprotein-releasing capacity of LolA, while interruption of smaller
patches apparently reduced efficiency. Thus, the results show a new lipoprotein transport
model that places (some of) the acyl chains on the hydrophobic surface patches.

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