Human sputum cathepsin B degrades proteoglycan, is inhibited by alpha 2-macroglobulin and is modulated by neutrophil elastase cleavage of cathepsin B precursor and cystatin C.
The high-Mr alkali-stable form of cathepsin B was purified from purulent human sputum. It was shown to solubilize proteoglycan monomer entrapped in polyacrylamide at a rate comparable with that of human lysosomal cathepsin B. Like the enzyme from lysosomes, sputum cathepsin B was bound by human alpha 2-macroglobulin, which inhibited its action on proteoglycan. Cystatin C in purulent sputum was shown to be the N-terminally truncated form generated by neutrophil elastase cleavage, and sputum cathepsin B was only weakly inhibited by recombinant cystatin C that had been cleaved by neutrophil elastase in vitro. Addition of neutrophil elastase to mucoid sputum led to a 5-fold increase in cathepsin B activity concomitant with a lowering in Mr of the cysteine proteinase from 40,000 to 37,000, i.e. the size of the active enzyme purified from purulent sputum. It is concluded that the high-Mr form of cathepsin B present in purulent sputum is a functional proteinase, unlike similar forms of the enzyme secreted by mammary gland in organ culture. The activity of cathepsin B in sputum is modulated by neutrophil elastase, by a combination of inhibitor inactivation and zymogen activation.
Buttle
D J
DJ
Department of Biochemistry, Strangeways Research Laboratory, Cambridge, U.K.
Abrahamson
M
M
Burnett
D
D
Mort
J S
JS
Barrett
A J
AJ
Dando
P M
PM
Hill
S L
SL
D000595:Amino Acid Sequence; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D055316:Cystatin C; D015891:Cystatins / Q000302:isolation & purification / Q000494:pharmacology*; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D019272:Leukocyte Elastase; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010196:Pancreatic Elastase / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D013183:Sputum / Q000201:enzymology*; D000511:alpha-Macroglobulins / Q000378:metabolism / Q000494:pharmacology*
C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D004792:Enzyme Precursors; D011509:Proteoglycans; D011994:Recombinant Proteins; D000511:alpha-Macroglobulins; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase; C057832:procathepsin B; D002401:Cathepsin B