SAXSdb — 8tcb

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1. Protein Identity and Related Structures Protein Identity & Related Structures

C4b-binding protein alpha chain

Homo sapiens

State in the Current Structure

Assembly	Physical composition	Protein state	Molecular copy count	Associated components	Data consistency
1	Protein heterocomplex	Heteromer	Protein 4	M protein × 2 （Q6TLP8） POTASSIUM ION × 1 water × 4	Consistent with protein count

Other States of the Same Protein in the Database

View Construct and Data Evidence

UniProt name	C4BPA_HUMAN
Isoform	—
PDB entities	1
Chains and sequence ranges	Author chain A； PDBConstruct 5–128； UniProt 49–172 Author chain B； PDBConstruct 5–128； UniProt 49–172

M protein

Streptococcus pyogenes

UniProt Q6TLP8

State in the Current Structure

Assembly	Physical composition	Protein state	Molecular copy count	Associated components	Data consistency
1	Protein heterocomplex	Heteromer	Protein 4	C4b-binding protein alpha chain × 2 （P04003） POTASSIUM ION × 1 water × 4	Consistent with protein count

Other States of the Same Protein in the Database

View Construct and Data Evidence

UniProt name	Q6TLP8_STRPY
Isoform	—
PDB entities	2
Chains and sequence ranges	Author chain C； PDBConstruct 5–104； UniProt 23–122 Author chain D； PDBConstruct 5–104； UniProt 23–122

The page prioritizes protein identity, the current assembly, associated components, oligomeric state and cross-PDB links. Chain mapping and sequence ranges are retained as data evidence. Internal IDs, import timestamps and assembly operation expressions are maintenance fields and are not shown here.

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2. Structure Basics 2. Structure Basics

Entry ID entry_id	8tcb
Deposition date deposition_date	2023-06-30
Last revision last_revision	2024-11-06
Structure title title	Structure of human C4b-binding protein alpha chain CCP domains 1 and 2 in complex with the hypervariable region of group A Streptococcus M87 protein
Keywords keywords	immune evasion, human complement, IMMUNE SYSTEM; IMMUNE SYSTEM
Experimental Method method	X-RAY DIFFRACTION

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3. Official assembly/model SAXS Official SAXS Profiles

This page reads only the latest assembly calculations. Every curve maps to an explicit PDB entry, official biological assembly and coordinate model.

8tcb__assembly_1__model_1

Assembly 1 · Model 1 · CRYSOL 4.1.3-1-20251215 (887e7ef)

Download this curve (.dat)

8tcb__assembly_1__model_1 | I(q)

100 plotted points; both axes use logarithmic scales.

8tcb__assembly_1__model_1 | P(r) · Pending

P(r) will be calculated and displayed separately for the same assembly/model.

Rg（Guinier）	27.99 Å
Rg (electron density)	27.77 Å
Total Rg	28.12 Å
Atom count	2676
Residues	379
Excluded volume	46489 Å³
Maximum q	0.500 Å⁻¹

Assembly	Model	Structure unit	Oligomeric description	Status	CRYSOL	Actions
1	1	`8tcb__assembly_1__model_1`	tetrameric （4）	Success	4.1.3-1-20251215 (887e7ef)	View Download

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4. Crystallography and Experiment 4. Crystallography & Experiment

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5. Entities and Polymers Entities & Polymers (4)

Entity 1 Entity 1 polymer

Description description	C4b-binding protein alpha chain
Molecular weight formula_weight	14163.9 kDa
Source method src_method	man
Copy count entity_count	2

Polymer Polymer

Polymer type type	polypeptide(L)
Chain IDs strand_id	A,B
Atom count atom_count	2705

GPGSNCGPPPTLSFAAPMDITLTETRFKTGTTLKYTCLPGYVRSHSTQTLTCNSDGEWVYNTFCIYKRCRHPGELRNGQVEIKTDLSFGSQIEFSCSEGFFLIGSTTSRCEVQDRGVGWSHPLPQCEI

Source Source

Source organism organism	Homo sapiens
Common name common_name	human
NCBI taxonomy ID ncbi_taxonomy_id	9606
Host organism host_organism	Escherichia coli

Entity 2 Entity 2 polymer

Description description	M protein
Molecular weight formula_weight	12531.7 kDa
Source method src_method	man
Copy count entity_count	2

Polymer Polymer

Polymer type type	polypeptide(L)
Chain IDs strand_id	C,D

GPGSESPREVTNELAASVWKKKVEEAKEKASKLEKQLEEAQKDYSEIEGKLEQFWHDYDKLEKENKEYASQLGKNQEEREKLELEYLRKSDEEYKEHQQYRQEQ

Source Source

Source organism organism	Streptococcus pyogenes
NCBI taxonomy ID ncbi_taxonomy_id	1314
Host organism host_organism	Escherichia coli

Entity 3 Entity 3 non-polymer

Description description	POTASSIUM ION
Molecular weight formula_weight	39.1 kDa
Source method src_method	syn
Copy count entity_count	1

Entity 4 Entity 4 water

Description description	water
Molecular weight formula_weight	18.0 kDa
Source method src_method	nat
Copy count entity_count	29

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Unit-cell length a length_a	43.176 Å
Unit-cell length b length_b	73.802 Å
Unit-cell length c length_c	190.398 Å
Unit-cell angle α angle_alpha	90.00 °
Unit-cell angle β angle_beta	90.00 °
Unit-cell angle γ angle_gamma	90.00 °
Molecules per unit cell Z z_pdb	8

Space group space_group	P 2 21 21
Space-group number int_tables_number	18
Crystal system crystal_system	orthorhombic

Resolution resolution	2.690 Å
Low-resolution limit resolution_low	68.810 Å
R factor r_factor	0.2375
R_work r_work	0.2353
R_free r_free	0.2784

Structure of human C4b-binding protein alpha chain CCP domains 1 and 2 in complex with the hypervariable region of group A Streptococcus M87 protein

1. Protein Identity and Related Structures Protein Identity & Related Structures

C4b-binding protein alpha chain

State in the Current Structure

Other States of the Same Protein in the Database

M protein

State in the Current Structure

Other States of the Same Protein in the Database

2. Structure Basics 2. Structure Basics

3. Official assembly/model SAXS Official SAXS Profiles

8tcb__assembly_1__model_1

8tcb__assembly_1__model_1 | I(q)

8tcb__assembly_1__model_1 | P(r) · Pending

4. Crystallography and Experiment 4. Crystallography & Experiment

Unit cell Unit Cell

Symmetry Symmetry

Refinement Refinement

Diffraction experiment Diffraction

5. Entities and Polymers Entities & Polymers (4)

Entity 1 Entity 1 polymer

Polymer Polymer

Source Source

Entity 2 Entity 2 polymer

Polymer Polymer

Source Source

Entity 3 Entity 3 non-polymer

Entity 4 Entity 4 water

7. Citations (1)

Structure of human C4b-binding protein alpha chain CCP domains 1 and 2 in complex with the hypervariable region of group A Streptococcus M87 protein

1. Protein Identity and Related Structures Protein Identity & Related Structures

C4b-binding protein alpha chain

State in the Current Structure

Other States of the Same Protein in the Database

Monomer

Homodimer

Homotetramer

Other homooligomers

Heteromeric or nucleic-acid complex

M protein

State in the Current Structure

Other States of the Same Protein in the Database

Monomer

Homodimer

Homotetramer

Other homooligomers

Heteromeric or nucleic-acid complex

2. Structure Basics 2. Structure Basics

3. Official assembly/model SAXS Official SAXS Profiles

8tcb__assembly_1__model_1

8tcb__assembly_1__model_1 | I(q)

8tcb__assembly_1__model_1 | P(r) · Pending

4. Crystallography and Experiment 4. Crystallography & Experiment

Unit cell Unit Cell

Symmetry Symmetry

Refinement Refinement

Diffraction experiment Diffraction

5. Entities and Polymers Entities & Polymers (4)

Entity 1 Entity 1 polymer

Polymer Polymer

Source Source

Entity 2 Entity 2 polymer

Polymer Polymer

Source Source

Entity 3 Entity 3 non-polymer

Entity 4 Entity 4 water

7. Citations (1)