The CUB domain (for complement C1r/C1s, Uegf, Bmp1) is a structural motif of approximately 110 residues found almost exclusively in extracellular and plasma membrane-associated proteins, many of which are developmentally regulated.
[1][2] These proteins are involved in a diverse range of functions, including complement activation, developmental patterning, tissue repair, axon guidance and angiogenesis, cell signalling, fertilisation, haemostasis, inflammation, neurotransmission, receptor-mediated endocytosis, and tumour suppression.
Spermadhesin is a subdivision of the CUB domain family and forms a major component of the mammalian seminal fluid.
[5] The spermadhesins from pigs, bulls and stallions show 40–98% similarity in their amino acid sequences and all possess a disulphide bond between adjacent cysteine residues.
For example, in the complement proteases, the CUB domains mediate dimerisation and binding to collagen-like regions of target proteins (e.g. C1q for C1r/C1s).