Sperm-egg fusion protein LLCFC1 (LLCFC1)

Sperm-egg fusion protein LLCFC1 (LLCFC1, also known as SOF1, C7orf34, CTM-1, and other aliases) is a sperm membrane protein that is **essential for the fusion of sperm and oocyte membranes during mammalian fertilization**[1][3][5]. This protein is **highly expressed in testis** and **localized to the sperm membrane**, becoming functionally important after the acrosome reaction that primes sperm for fusion with the oocyte[3]. Genetic knockout studies in mice show that loss of LLCFC1/SOF1 causes complete infertility due to sperm failing to fuse with eggs, even though sperm morphology and binding are normal[3][5]. SOF1 acts together with other sperm proteins such as IZUMO1, TMEM95, and SPACA6 in the membrane fusion complex, but is **not itself a receptor, enzyme, or canonical drug target**. No pharmacological ligands, biomarkers, or direct clinical relevance as a therapeutic target are known, and it is not recognized as a disease target outside of experimental models of infertility[1][3][5]. Key details: - **Gene location**: Chromosome 7 (human); gene symbol LLCFC1, formerly C7orf34[1][4]. - **Protein function**: Facilitates the actual fusion stage of fertilization, a step critical for successful conception[3][5]. - **Current therapeutic relevance**: *Not a therapeutic target* in current drug discovery, but may be a candidate for non-hormonal male contraception or as a biomarker in rare infertility investigations[3][5]. No drugs are known to interact with LLCFC1, and no established mechanisms of drug action for this protein exist. No safety or biomarker data is available. The molecule is best classified as an essential **gamete fusion factor** in reproductive biology[3][5].

Other names

C7orf34SOF1CTM-1LLLL and CFNLAS motif containing 1MSSP-binding protein CTM-1sperm-oocyte fusion required protein 1sperm-oocyte fusion required 1uncharacterized protein C7orf34