Effect of the Z mutation on the physical and inhibitory properties of alpha 1-antitrypsin.
A major feature of the structure of alpha 1-antitrypsin is a five-stranded A-sheet into which the reactive center loop inserts after cleavage. We describe here the effect of the Z mutation (342Glu to Lys) at the head of the fifth strand of the A-sheet on the mobility of the reactive center loop and hence on the physical properties of the antitrypsin molecule. The mutant Z but not the normal M antitrypsin spontaneously polymerizes at 37 degrees C by a mechanism involving the insertion of the reactive center loop of one molecule into the A-sheet of a second. It is demonstrated that Z antitrypsin polymerized after incubation with 1.0 M guanidinium chloride at 37 degrees C at the same rate as M antitrypsin. Reducing the temperature to 4 degrees C favored the formation of the L-state in M antitrypsin in which the loop is stably incorporated into the A-sheet, but resulted in loop-sheet polymerization in Z antitrypsin. Z, like M antitrypsin, undergoes the S to R transition, but we show that the accompanying change in thermal stability results from loop-sheet polymerization (S) which can be prevented by the insertion of the cleaved strand of the reactive center loop into the A-sheet (R). Z antitrypsin has a reduced association rate constant with neutrophil elastase [(5.3 +/- 0.06) x 10(7) and (1.2 +/- 0.02) x 10(7) M-1 s-1 for M and Z, respectively], but both M and Z antitrypsin had Ki values of less than 5 pM.(ABSTRACT TRUNCATED AT 250 WORDS)
Lomas
D A
DA
Department of Haematology, University of Cambridge, MRC Centre, U.K.
Evans
D L
DL
Stone
S R
SR
Chang
W S
WS
Carrell
R W
RW
D000595:Amino Acid Sequence; D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism; D002942:Circular Dichroism; D006358:Hot Temperature; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D019272:Leukocyte Elastase; D008969:Molecular Sequence Data; D009154:Mutation; D010196:Pancreatic Elastase / Q000037:antagonists & inhibitors; D011108:Polymers / Q000737:chemistry; D000515:alpha 1-Antitrypsin / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
D011108:Polymers; C043392:SERPINA1 protein, human; D000515:alpha 1-Antitrypsin; D002918:Chymotrypsin; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase