Am. J. Respir. Cell Mol. Biol., Vol 15, No. 2, 08 1996, 283-291.
Alginate, the slime exopolysaccharide of Pseudomonas aeruginosa, binds human leukocyte elastase, retards inhibition by alpha 1-proteinase inhibitor, and accelerates inhibition by secretory leukoprotease inhibitor
QL Ying, M Kemme and SR Simon
Department of Pathology, State University of New York at Stony Brook 11794, USA.
The interaction of alginate from Pseudomonas aeruginosa ATCC 39324 with
human leukocyte elastase was studied by determining the effects of the
polysaccharide on the amidolytic activity of the enzyme toward a range of
synthetic peptide substrates of different length. The data support a model
in which each elastase molecule interacts with a total of 19 uronic acid
units on the alginate, primarily through electrostatic forces. Binding of
alginate results in occlusion of distal subsites, most likely S4 and S5, of
the enzyme's extended substrate-binding domain. As a result, alginate alone
appears to be a weak inhibitor of the hydrolysis of long synthetic peptide
substrates and [14C]elastin by elastase. Alginate also has effects on the
antielastase function of naturally occurring protease inhibitors in the
lung: It reduces the association rate of elastase and alpha 1-proteinase
inhibitor, whereas it increases the association rate of elastase and
secretory leukoprotease inhibitor. In the presence of 36 micrograms/ml
alginate, the median concentration found in sputum from cystic fibrosis
patients infected with mucoid strains of P. aeruginosa, the second-order
rate constant for inhibition of elastase by secretory leukoprotease
inhibitor is 2.6-fold greater than that for alpha 1-proteinase inhibitor.
Alginate has only a minor effect on the antielastase activities of elafin
and a recombinant form of the isolated C-terminal domain of secretory
leukoprotease inhibitor. Based on these findings, alginate may be an
important factor in determining the local distribution of leukocyte
elastase and perturbing the overall protease- antiprotease balance in the
infected lungs of cystic fibrosis patients.
