The molecular chaperone cysteine string protein is required for monomeric SNARE proteins to assemble in trans-complexes during human sperm acrosomal exocytosis

• Published in: Biology of reproduction Vol. 108; no. 2; pp. 1 - 12
• Main Authors: Flores-Montero, Karina, Berberián, María Victoria, Mayorga, Luis Segundo, Tomes, Claudia Nora, Ruete, María Celeste
• Format: Journal Article
• Language: English
• Published: United States Society for the Study of Reproduction 13.02.2023; Oxford University Press
• Subjects: acrosomal exocytosis; Acrosome - metabolism; Cell fusion; Chaperones; Cysteine; cysteine string protein; Exocytosis; Exocytosis - physiology; Hsp40 protein; human sperm; Humans; Immunofluorescence; Infertility; Male; Membrane fusion; Plasma membranes; Proteins; RESEARCH ARTICLE; Semen - metabolism; SNAP receptors; SNARE Proteins - metabolism; SNAREs; Sperm; Spermatogenesis; Spermatozoa - metabolism; String protein; Transmission electron microscopy; human sperm; cysteine string protein; chaperones; SNAREs; acrosomal exocytosis
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1093/biolre/ioac196

Membrane fusion in sperm cells is crucial for acrosomal exocytosis and must be preserved to ensure fertilizing capacity. Evolutionarily conserved protein machinery regulates acrosomal exocytosis. Molecular chaperones play a vital role in spermatogenesis and post-testicular maturation. Cysteine string protein (CSP) is a member of the Hsp40 co-chaperones, and the participation of molecular chaperones in acrosomal exocytosis is poorly understood. In particular, the role of CSP in acrosomal exocytosis has not been reported so far. Using western blot and indirect immunofluorescence, we show that CSP is present in human sperm, is palmitoylated, and predominantly bound to membranes. Moreover, using functional assays and transmission electron microscopy, we report that blocking the function of CSP avoided the assembly of transcomplexes and inhibited exocytosis. In summary, here, we describe the presence of CSP in human sperm and show that this protein has an essential role in membrane fusion during acrosomal exocytosis mediating the trans-SNARE complex assembly between the outer acrosomal and plasma membranes. In general, understanding CSP's role is critical in identifying new biomarkers and generating new rational-based approaches to treat male infertility. Summary Sentence: Cysteine string protein is necessary and mediates the trans-SNARE complexes assembly between the outer acrosomal and the plasma membranes in human sperm acrosomal exocytosis mechanism. Graphical Abstract