The members of the avidin protein family are well known for their high affinity towards D-biotin and their structural stability. These properties make avidins a valuable tool for various biotechnological applications. In the present study, two avidin-like biotin-binding proteins (named streptavidin C1 and C2) from Streptomyces cinnamonensis were newly identified while exploring antifungal proteins against Fusarium oxysporum f. sp. cucumerinum. Streptavidin C1 reveals a low correlation (a sequence identity of approximately 64%) with all known streptavidins, whereas streptavidin C2 shares a sequence identity of approximately 94% with other streptavidins. Here, the crystal structures of streptavidin C1 in the mature form and in complex with biotin at 2.1 and 2.5 Å resolution, respectively, were assessed. The overall structures present similar tetrameric features with D ₂ symmetry to other (strept)avidin structures. Interestingly, the long C-terminal region comprises a short α-helix (C-Lid; residues 169–179) and an extension C-terminal peptide (ECP; residues 180–191) which stretches into the biotin-binding sites of the same monomer. This ECP sequence (–¹⁸⁰VTSANPPAS¹⁸⁸–) is a newly defined biotin-binding site, which reduces the ability to bind to (strept)avidin family proteins. The novel streptavidin C1 could help in the development of an engineered tetrameric streptavidin with reduced biotin-binding capacity as well as other biomaterial tools.

Strawberry (Fragaria × ananassa Duch.) is susceptible to viral disease accumulation due to its vegetative propagation through runners. This study evaluated the incidence and distribution of major strawberry viruses in Korea at both the cultivar and regional levels. We collected 333 leaf samples from three commercial cultivars (‘Seolhyang,’ ‘Kuemsil,’ and ‘King’s Berry’) across four major strawberry-producing regions between November 2023 and February 2024. The samples were analysed using standardized singleplex RT-PCR assays targeting nine strawberry viruses. Overall, the incidence of viruses was low, with Strawberry mottle virus (SMoV) detected in 4.2% of samples and Strawberry mild yellow edge virus (SMYEV) in 2.7%. Strawberry necrotic shock virus (SNSV) and Arabis mosaic virus (ArMV) were found sporadically, while the other viruses were not detected. The ‘King’s Berry’ cultivar exhibited the highest infection rate, with mixed infections occurring more frequently in this variety. Regional variations in virus incidence correlated with cultivation density and management practices. These findings suggest that while strawberry virus occurrence in Korea remains limited, it varies by cultivar and region, highlighting the need for ongoing monitoring - particularly of SMoV and SMYEV - as part of virus management programs.