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An acidic
amino acid-specific protease from germinating soybeans.
Phytochemistry 1996 May;42(2):313-9
Tan-Wilson AL, Liu X, Chen R, Qi X, Wilson KA.
Department of Biological Sciences, State University of New York at Binghamton
13902-6000, USA.
The degradation of the beta-conglycinin protein reserves in soybean seeds during
germination and early growth begins with the proteolysis of its alpha and alpha'
subunits by an enzyme called Protease C1. In the pathway, a number of
proteolytic intermediates are produced and subsequently degraded. Determination
of the N-terminal sequences of these intermediates provides insight regarding
the requirements of the cleavage sites. The N-terminal sequence of three such
proteolytic intermediates has been determined. The sequence has been located in
the published sequences of the beta-conglycinin subunits. Comparing these
cleavage sites, plus those of two others previously delineated, shows that the
P1' and P4' positions always bear either a Glu or an Asp residue while the P1
position always bears either a Glu or a Gln residue. In addition, other sites
from P3 to P7' are also rich in either Glu or Asp, and the whole region is
predicted to be in a alpha-helix. Consistent with the observation, synthetic
poly-L-Glu inhibits the Protease C1-catalysed degradation of the alpha and
alpha' subunits of beta-conglycinin. Poly-L-Glu (av. M(r) = 1000) at 12.5 mM was
more effective at inhibiting the reaction than poly-L-Glu (av. M(r) = 600) or
poly-L-Glu (av. M(r) = 14,300) at the same concentration. Comparing large
synthetic polypeptides at 12.5mM, inhibition by poly-L-Asp (av. M(r) = 15,000)
is as effective as poly-L-Glu (av. M(r) = 14,300), while poly-L-Ser (av. M(r) =
15,000) had no effect at all. Poly-D-Glu (av. M(r) = 15,000) is a better
inhibitor than poly-L-Glu of the same size. A serine protease of similar
molecular weight as Protease C1 and also capable of catalysing the proteolysis
of the alpha and alpha' subunits of beta-conglycinin to generate proteolytic
intermediates of the same size has been found in mung bean.
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