Corn Kernel cysteine proteinase inhibitor as a novel cystatin superfamily member of plant origin: Molecular cloning and expression studies

Abstract

A full‐length cDNA clone for a cysteine proteinase inhibitor (cystatin) was isolated from a λgt10 cDNA library of immature corn kernels by screening with a mixture of cDNA inserts for oryzacystatins I and II. The cDNA clone spans 960 base pairs, encoding a 135‐amino‐acid protein containing a signal peptide fragment. The protein, named corn cystatin I, is considered to be a member of the cystatin superfamily, since it contains the commonly conserved Gln‐Val‐Val‐Ala‐Gly region that exists in most known cystatins as a probable binding site and is significantly similar to other cystatins in its overall amino acid sequence. Corn cystatin I expressed in Escherichia coli showed a strong papain‐inhibitory activity. Northern blot analysis showed that the amount of mRNA for corn cystatin I reaches a maximum 2 weeks after flowering and then decreases gradually. Copyright © 1992, Wiley Blackwell. All rights reserved