TY - JOUR

T1 - Human lysozyme peptidase resistance is perturbed by the anionic glycolipid biosurfactant rhamnolipid produced by the opportunistic pathogen Pseudomonas aeruginosa

AU - Andersen, Kell K

AU - Vad, Brian Stougaard

AU - Scavenius, Carsten

AU - Enghild, Jan Johannes

AU - Otzen, Daniel Erik

PY - 2017

Y1 - 2017

N2 - Infection by the opportunistic pathogen Pseudomonas aeruginosa (PA) is accompanied by the secretion of virulence factors such as the secondary metabolite rhamnolipid (RL) as well as an array of bacterial enzymes, including the protease elastase. The human immune system tries to counter this via defensive proteins such as human lysozyme (HLZ). HLZ targets the bacterial cell wall but may also have other antimicrobial activities. The enzyme contains four disulfide bonds and shows high thermodynamic stability and resistance to proteolytic attack. Here we show that RL promotes HLZ degradation by several unrelated proteases, including the PA elastase and human proteases. This occurs although RL does not by itself denature HLZ. Nevertheless, RL binds in a sufficiently high stoichiometry (8 RL:1 HLZ) to neutralize the highly cationic surface of HLZ. The initial cleavage sites agree well with the domain boundaries of HLZ. Thus, RL binding to native HLZ may be sufficient to allow proteolytic attack at slightly exposed sites on the protein, leading to subsequent degradation. Furthermore, biofilms of RL-producing strains of PA are protected better against high concentrations of HLZ than RL-free PA strains. We conclude that pathogen-produced RL may weaken host defenses by facilitating degradation of key host proteins.

AB - Infection by the opportunistic pathogen Pseudomonas aeruginosa (PA) is accompanied by the secretion of virulence factors such as the secondary metabolite rhamnolipid (RL) as well as an array of bacterial enzymes, including the protease elastase. The human immune system tries to counter this via defensive proteins such as human lysozyme (HLZ). HLZ targets the bacterial cell wall but may also have other antimicrobial activities. The enzyme contains four disulfide bonds and shows high thermodynamic stability and resistance to proteolytic attack. Here we show that RL promotes HLZ degradation by several unrelated proteases, including the PA elastase and human proteases. This occurs although RL does not by itself denature HLZ. Nevertheless, RL binds in a sufficiently high stoichiometry (8 RL:1 HLZ) to neutralize the highly cationic surface of HLZ. The initial cleavage sites agree well with the domain boundaries of HLZ. Thus, RL binding to native HLZ may be sufficient to allow proteolytic attack at slightly exposed sites on the protein, leading to subsequent degradation. Furthermore, biofilms of RL-producing strains of PA are protected better against high concentrations of HLZ than RL-free PA strains. We conclude that pathogen-produced RL may weaken host defenses by facilitating degradation of key host proteins.

U2 - 10.1021/acs.biochem.6b01009

DO - 10.1021/acs.biochem.6b01009

M3 - Journal article

C2 - 27931094

VL - 56

SP - 260

EP - 270

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 1

ER -