_EC 3.4.21.42 Complement subcomponent C1s. 5 PDB entries  
EC 3.-.-.- Hydrolases. [19,580 PDB entries]
EC 3.4.-.- Acting on peptide bonds (peptide hydrolases). [6,506 PDB entries]
EC 3.4.21.- Serine endopeptidases. [2,457 PDB entries]
EC 3.4.21.42 Complement subcomponent C1s. [5 PDB entries]    
1elv

Reaction: Cleavage of Arg-|-Ala bond in complement component C4 to form C4a and C4b, and Lys(or Arg)-|-Lys bond in complement component C2 to form C2a and C2b: the 'classical' pathway C3 convertase.
Other name(s): C1s esterase.
Comments: Activated from proenzyme C1s in plasma by the activated complement subcomponent C1r. Belongs to peptidase family S1.
Links:   [IntEnz]   [ExPASy]   [KEGG]  

There are 5 PDB entries in enzyme class E.C.3.4.21.42

  PDB code Protein
1elv
Crystal structure of the catalytic domain of human complemen protease
Source: Homo sapiens. Human. Organism_taxid: 9606. Expressed in: spodoptera frugiperda. Expression_system_taxid: 7108. Expression_system_cell_line: sf21. Other_details: bac-to-bac expression system
Chain: A (303 residues) CATH domains: 2.40.10.10 2.40.10.10 2.10.70.10
1nzi
Crystal structure of the cub1-egf interaction domain of complement protease c1s
Source: Homo sapiens. Human. Organism_taxid: 9606. Gene: c1s. Expressed in: trichoplusia ni. Expression_system_taxid: 7111. Expression_system_cell_line: high five insect cells.
Chains: A, B (155 residues) CATH domains: 2.60.120.290 2.10.25.10
4j1y
The x-ray crystal structure of human complement protease c1s
Source: Homo sapiens. Human. Organism_taxid: 9606. Gene: c1s. Expressed in: escherichia coli. Expression_system_taxid: 562.
Chains: A, B (378 residues) CATH domains: Unassigned 2.40.10.10 2.40.10.10
4lmf
C1s cub1-egf-cub2
Source: Homo sapiens. Human. Organism_taxid: 9606. Gene: c1s. Expressed in: cricetulus griseus. Expression_system_taxid: 10026
Chains: A, B, C, D (276 residues) CATH domains: 2.60.120.290 2.10.25.10 2.60.120.290
4lor
C1s cub1-egf-cub2 in complex with a collagen-like peptide fr
Source: Homo sapiens. Human. Organism_taxid: 9606. Gene: c1s. Expressed in: cricetulus griseus. Expression_system_taxid: 10026. Synthetic: yes
Chain: A (276 residues) CATH domains: 2.60.120.290 2.10.25.10 2.60.120.290