PROSITE documentation PDOC51473

Gnk2-homologous domain profile

Ginkbilobin-2 (Gnk2) is an antifungal protein found in the endosperm of Ginkgo seeds, which inhibits the growth of phytopathogenic fungi such as Fusarium oxysporum. Gnk2 has considerable homology (~85%) to embryo-abundant proteins (EAP) from the gymnosperms Picea abies and P. glauca. Plant EAP are expressed in the late stage of seed maturation and are involved in protection against environmental stresses such as drought. The sequence of Gnk2 is also 28-31% identical to the extracellular domain of cysteine-rich receptor-like kinases (CRK) from the angiosperm Arabidopsis. The CRK members are induced by pathogen infection and treatment with reactive oxygen species or salicylic acid and are involved in the hypersensitive reaction, which is a typical system of programmed cell death. In addition, there are at least 60 genes in Arabidopsis encoding the cysteine-rich secreted proteins (CRSP) with an Gnk2-homologous domain. Therefore, the proteins with a Gnk2-homologous domain are regarded as one of the largest protein superfamilies, although the role of the conserved Gnk2-homologous domain remains unclear [1,2].

The Gnk2-homologous domain is composed of two α-helices and a five stranded β-sheet, which forms a compact single-domain architecture with an α+β-fold (see <PDB:3A2E>). It contains a C-X(8)-C-X(2)-C motif. Cysteine residues form three intramolecular disulfide bridges: C1-C5, C2-C3, and C4-C6 [1].

The profile we developed covers the entire Gnk2-homologous domain.