C1s deficiency

Gene Information


HUGO name: C1S


  • Complement component 1, s subcomponent
  • Complement C1s component precursor (C1 esterase)


Reference sequences

Chromosomal location


Protein Information


Protein function:

C1s b chain is a serine protease that combines with C1q and C1s to form C1, the first component of the classical pathway of the complement system. C1r activates C1s so that it can, in turn, activate C2 and C4.

Catalytic activity:

Cleaves component C4 to C4a and C4b, and component C2 to C2a and C2b.


C1 is a calcium-dependent trimolecular complex of C1q, r and s in the molar ration of 1:2:2. Activated C1s is an disulfide-linked heterodimer of an heavy chain and a light chain.

Structures (PDB)


Expression pattern for human

Tissue Expression (%) Clones
connective tissue 9.43 3:1301
thyroid gland 7.20 2:1136
nasopharynx 6.33 1:646
subchondral bone 6.14 2:1332
brain, meningioma 5.77 1:709
adipose 4.82 1:849
pancreas, exocrine 4.39 23:21418
mammary gland 2.84 1:1441
esophagus 2.77 2:2949
lung with fibrosis 2.77 1:1479

Animal models


C. elegans