Table II. Structural comparisons of the C1s SP domain with homologous X-ray structures.

A Overall structure
	Chymotrypsin	Thrombin	Factor Xa	Trypsin	Protein C
Global r.m.s. (Å)/nb Ca	1.0/194	0.8/182	1.0/188	0.8/183	1.0/194
Sequence identity (%)	37	38	35	36	37
PDB code	3gch	1fpc	1fax	1trn	1aut
B Surface segments of the C1s SP domain significantly different (d >1.5 Å) from the homologous segments of other SP domains (chymotrypsin,trypsin, thrombin, factor VII, factor D, factor Xa, and factor IXa)

C1s numbering	Chymotrypsin numbering	Loop labela	Type of modification
430–431	23–24		same length
441–443	34–40	A	deletion
466–467	61–62	B	variable
501–509	96–98	C	major insertion
538–543	126–129		minor insertion
560–562	145–146	D	variable
577–596	165–175	3	major insertion
607–608	185–187	1	deletion
625–630	203–205		minor insertion
646	221–224	2	deletion

^aLoop labels as defined by Perona and Craik (1997) and detailed in Figure 2A. Loop E is not defined in C1s structure.