9T47

Structure of the SUN4 domain from Saccharomyces cerevisiae

Summary for 9T47

• Entry DOI: 10.2210/pdb9t47/pdb
• Descriptor: Probable secreted beta-glucosidase SUN4, HEXAETHYLENE GLYCOL (3 entities in total)
• Functional Keywords: cell wall, carbohydrate-binding, thaumatin-like domain, structural protein
• Biological source: Saccharomyces cerevisiae S288C
• Total number of polymer chains: 1
• Total formula weight: 31476.10

Authors

Weitzel, V.,Veelders, M.,Moesch, H.-U.,Essen, L.-O. (deposition date: 2025-10-30, release date: 2026-02-18, Last modification date: 2026-05-20)

Primary citation

Schoppner, P.,Weitzel, V.,Veelders, M.,Korf, L.,Andras, J.,Wolf, K.,Bruckner, S.,Essen, L.-.O.,Mosch, H.-.U.
Structural evolution of a fungal cell wall protein family for beta-glucan-binding and cell separation.
Mbio, :e0353525-e0353525, 2026

PubMed Abstract: In fungi, the continuous biosynthesis and remodeling of the cell wall are crucial for growth, division, and development. A hallmark of fungal cell walls is their layered structure, which includes several carbohydrate polymers, such as β-glucans, and a large number of associated cell wall proteins. The fungal-specific family of SUN domain proteins has been implicated in cell wall remodeling and cell separation, but detailed structure-based analyses revealing precise molecular functions have been lacking until now. In this study, we determined high-resolution crystal structures of the SUN domains from two paralogs of the SUN family in budding yeast. We find that their bilobal architecture consists of a domain with high structural similarity to the Sushi/SCR/CCP domain (INTERPRO family IPR000436), and an intimately associated thaumatin-like domain (IPR001938). Together, these domains form a highly conserved canyon fitted to accommodate both single- and triple-helical β-glucan polymers. Within this canyon, we identify 12 conserved polar residues that are crucial for the function of SUN domains in mediating cell separation. We further demonstrate that SUN domains are functionally interchangeable between paralogs in budding yeast, as well as between orthologs from budding yeast and phylogenetically distant fission yeast or filamentous fungi. We conclude that the fungal SUN domain family represents a unique class of β-1,3-glucan-binding proteins involved in cell wall remodeling and separation, whose successful evolution was enabled by the fusion of ancestral sushi- and thaumatin-like domains.

PubMed: 42089631
DOI: 10.1128/mbio.03535-25

Experimental method

X-RAY DIFFRACTION (1.1 Å)