The three‐dimensional structure of the bifunctional proteinase k/α‐amylase inhibitor from wheat (PKI3) at 2.5 Å resolution

Abstract

Wheat germ contains an inhibitor for proicinase K, called PK13 (M 1 ∼ 19600) which simultaneously inhibits α‐amylase. PK13 was crystallized, space group P21, α = 43.02 (5) Å, n = 65.18 (7) Å, c = 32.33 (4) Å, β = 112.79 (9), X‐ray data were collected to 2.5 Å resolution, the structure solved by molecular replacement on the basis of the atomic coordinates of the homologous Erythrina caffra DE‐3 inhibitor, and refined with simulated annealing techniques with a current R‐factor of 21%. The three‐dimensional structure of PK13 is stabilized by two disulfide bridges and has a central β‐barrel with distorted β‐structure. In analogy to related inhibitors, the binding site for proteinase K is assumed to be located on the surface of the protein (amino acids residues 66–67), although the 75–76 peptide bond is cleaved upon binding.

Tri-domain Bifunctional Inhibitor of Metallocarboxypeptidases A and Serine Proteases Isolated from Marine Annelid Sabellastarte magnifica

“…For example, ShPI-1, an inhibitor isolated from the sea anemone S. helianthus by the present authors (17), consists of a single domain able to inhibit serine, cysteine, and aspartic proteases. The same applies to an inhibitor of serine and metalloendoproteases isolated from Streptomyces caespitosus (75), an inhibitor of serine and aspartic proteases from Prosopis juliflora (76) and two inhibitors of serine proteases and amylase from barley and wheat (77,78), all of which act through different nonoverlapping binding sites. Bifunctional properties have also been observed in equistatin, an inhibitor with three thyroglobulin I domains, which inhibit cysteine and aspartic proteases (18,19).…”

The primary structure of inhibitor of cysteine proteinases from potato

“…The superfamily of ST1 would thus comprise proteins which have inhibitory activity against serine proteinases (trypsin and subtilisin family), aspartic proteinases (inhibitors active against cathepsin D), cysteine proteinases (inhibitors to papain family) and proteins with some other activity or function, like MRC with its sweet taste-modifying activity, or plant albumin, presumably functioning as a storage protein. Some of the members have multiple activities, like in~bition of serine and aspartic proteinases (NID, [IO]) or inhibition of a-amylase and subtilisin [32].…”

“…3) in ST1 and ETI, lysine is positioned in PCPI 8.3. In the case of WASI this is also the site, located at the active site of proteinase K [32]. Conformation of the reactive loop in STI-type of trypsin inhibitors is conserved by a hydrogen bonding network [31].…”

Analysis of the Complex Formed by Erythrina variegata Chymotrypsin Inhibitor with Chymotrypsin and Properties of the Peptides Prepared from the Inhibitor by a Limited Proteolysis

“…The two peptides have been obtained by cleavage at the single peptide bond between LyslO7-Thrl08. At present, the tertiary structures of Kunitz family proteins were established for STI [I], trypsin inhibitor from E. caffra (ETI) [23], and proteinase Wu-amylase inhibitor from wheat germ [24]; they all fold in a conserved conformation. Examining the structure of ETI corresponding to LyslO7 in ECI, the cleavage site (Glu105 in ETI) can be localized in the loop between &strands B3 and B4 (Fig.…”