Characterization of membrane N-glycan binding sites of lysozyme for cardiac depression in sepsis.
OBJECTIVE
In sepsis, reversible myocardial depression has been ascribed to the release of mediators of inflammation. We previously found that lysozyme released from leukocytes from the spleen and other organs mediated myocardial depression in an Escherichia coli model of septic shock in dogs. We hypothesize that lysozyme binds to or cleaves a cardiac surface membrane N-glycoprotein to cause depression. The objectives of the present study were: 1) to determine whether the binding of lysozyme is reversible; 2) to assess the N-glycan structure to which lysozyme binds; 3) to examine whether nonenzymatic proteins, termed lectins, with a binding specificity similar to that of lysozyme could also cause depression; and 4) to assess whether the membrane to which lysozyme binds is affected by the enzymes protease type XIV and collagenase A, that are used to prepare single cell myocyte experiments.


METHODS
We measured isometric contraction in a right ventricular trabecular preparation.


RESULTS
We found that lysozyme binds in a reversible manner to the Man beta(1-4) GlcNAc beta(1-4)GlcNAc moiety in the tri-mannosyl core structure of high mannose/hybrid and tri-antennary carbohydrate classes where GlcNAc is N-acetylglucosamine and Man is mannose. Lectins with a specificity similar to that of lysozyme also caused depression, and lysozyme's depressant activity was eliminated by protease type XIV and collagenase A.


CONCLUSIONS
These results indicate that lysozyme reversibly binds to a membrane glycoprotein to cause myocardial depression in sepsis. We further localize its binding site to a variant of the chitotriose structure in the tri-mannosyl core of the membrane glycoprotein.
Jacobs
Hans
H
Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada.
Mink
Steven N
SN
Duke
Krika
K
Bose
Deepak
D
Cheng
Zhao-Qin
ZQ
Howlett
Susan
S
Ferrier
Gregory R
GR
Light
R Bruce
RB
D000818:Animals; D001665:Binding Sites; D009202:Cardiomyopathies / Q000209:etiology; D004285:Dogs; D037102:Lectins / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009113:Muramidase / Q000378:metabolism*; D009200:Myocardial Contraction / Q000187:drug effects; D009844:Oligosaccharides / Q000378:metabolism*; D012772:Shock, Septic / Q000378:metabolism*
D037102:Lectins; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; D009113:Muramidase