2g9h

Crystal Structure of Staphylococcal Enterotoxin I (SEI) in Complex with a Human MHC class II Molecule

Method: X-RAY DIFFRACTION

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

HLA class II histocompatibility antigen, DR alpha chain

Homo sapiens

UniProt P01903

State in the Current Structure

Assembly	Physical composition	Protein state	Molecular copy count	Associated components	Data consistency
1	Protein heterocomplex	Heteromer	Protein 4	HLA class II histocompatibility antigen, DRB1-1 beta chain × 1 （P04229） Hemagglutinin × 1 （P04664） extracellular enterotoxin type I × 1 （O85383） SULFATE ION × 4 4-(2-HYDROXYETHYL)-1-PIPERAZINE ETHANESULFONIC ACID × 1 1,4-DIETHYLENE DIOXIDE × 2 ZINC ION × 1 water × 4	Consistent with protein count

Other States of the Same Protein in the Database

View Construct and Data Evidence

UniProt name	2DRA_HUMAN
Isoform	—
PDB entities	1
Chains and sequence ranges	Author chain A； PDBConstruct 1–182； UniProt 26–207

HLA class II histocompatibility antigen, DRB1-1 beta chain

Homo sapiens

UniProt P04229

State in the Current Structure

Assembly	Physical composition	Protein state	Molecular copy count	Associated components	Data consistency
1	Protein heterocomplex	Heteromer	Protein 4	HLA class II histocompatibility antigen, DR alpha chain × 1 （P01903） Hemagglutinin × 1 （P04664） extracellular enterotoxin type I × 1 （O85383） SULFATE ION × 4 4-(2-HYDROXYETHYL)-1-PIPERAZINE ETHANESULFONIC ACID × 1 1,4-DIETHYLENE DIOXIDE × 2 ZINC ION × 1 water × 4	Consistent with protein count

Other States of the Same Protein in the Database

View Construct and Data Evidence

UniProt name	2B11_HUMAN
Isoform	—
PDB entities	2
Chains and sequence ranges	Author chain B； PDBConstruct 1–190； UniProt 30–219

Hemagglutinin

OrganismNot specified

UniProt P04664

State in the Current Structure

Assembly	Physical composition	Protein state	Molecular copy count	Associated components	Data consistency
1	Protein heterocomplex	Heteromer	Protein 4	HLA class II histocompatibility antigen, DR alpha chain × 1 （P01903） HLA class II histocompatibility antigen, DRB1-1 beta chain × 1 （P04229） extracellular enterotoxin type I × 1 （O85383） SULFATE ION × 4 4-(2-HYDROXYETHYL)-1-PIPERAZINE ETHANESULFONIC ACID × 1 1,4-DIETHYLENE DIOXIDE × 2 ZINC ION × 1 water × 4	Consistent with protein count

Other States of the Same Protein in the Database

View Construct and Data Evidence

UniProt name	HEMA_IAEN6
Isoform	—
PDB entities	3
Chains and sequence ranges	Author chain C； PDBConstruct 1–13； UniProt 306–318

extracellular enterotoxin type I

OrganismNot specified

UniProt O85383

State in the Current Structure

Assembly	Physical composition	Protein state	Molecular copy count	Associated components	Data consistency
1	Protein heterocomplex	Heteromer	Protein 4	HLA class II histocompatibility antigen, DR alpha chain × 1 （P01903） HLA class II histocompatibility antigen, DRB1-1 beta chain × 1 （P04229） Hemagglutinin × 1 （P04664） SULFATE ION × 4 4-(2-HYDROXYETHYL)-1-PIPERAZINE ETHANESULFONIC ACID × 1 1,4-DIETHYLENE DIOXIDE × 2 ZINC ION × 1 water × 4	Consistent with protein count

Other States of the Same Protein in the Database

View Construct and Data Evidence

UniProt name	O85383_STAAU
Isoform	—
PDB entities	4
Chains and sequence ranges	Author chain D； PDBConstruct 1–218； UniProt 25–242

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	2g9h
Deposition date deposition_date	2006-03-06
Structure title title	Crystal Structure of Staphylococcal Enterotoxin I (SEI) in Complex with a Human MHC class II Molecule
Keywords keywords	Immune System, Superantigen, Zn, HLA clasII molecule; 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.

2g9h__assembly_1__model_1

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

Download this curve (.dat)

2g9h__assembly_1__model_1 | I(q)

100 plotted points; both axes use logarithmic scales.

2g9h__assembly_1__model_1 | P(r) · Pending

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

Rg（Guinier）	30.71 Å
Rg (electron density)	30.24 Å
Total Rg	30.85 Å
Atom count	4904
Residues	594
Excluded volume	86938 Å³
Maximum q	0.500 Å⁻¹

Assembly	Model	Structure unit	Oligomeric description	Status	CRYSOL	Actions
1	1	`2g9h__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 (9)

Entity 1 Entity 1 polymer

Description description	HLA class II histocompatibility antigen, DR alpha chain
Molecular weight formula_weight	21155.9 kDa
Source method src_method	man
Copy count entity_count	1

Polymer Polymer

Polymer type type	polypeptide(L)
Chain IDs strand_id	A
Atom count atom_count	5364

IKEEHVIIQAEFYLNPDQSGEFMFDFDGDEIFHVDMAKKETVWRLEEFGRFASFEAQGALANIAVDKANLEIMTKRSNYTPITNVPPEVTVLTNSPVELREPNVLICFIDKFTPPVVNVTWLRNGKPVTTGVSETVFLPREDHLFRKFHYLPFLPSTEDVYDCRVEHWGLDEPLLKHWEFDA

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 BL21(DE3)

Entity 2 Entity 2 polymer

Description description	HLA class II histocompatibility antigen, DRB1-1 beta chain
Molecular weight formula_weight	22080.7 kDa
Source method src_method	man
Copy count entity_count	1

Polymer Polymer

Polymer type type	polypeptide(L)
Chain IDs strand_id	B

GDTRPRFLWQLKFECHFFNGTERVRLLERCIYNQEESVRFDSDVGEYRAVTELGRPDAEYWNSQKDLLEQRRAAVDTYCRHNYGVGESFTVQRRVEPKVTVYPSKTQPLQHHNLLVCSVSGFYPGSIEVRWFRNGQEEKAGVVSTGLIQNGDWTFQTLVMLETVPRSGEVYTCQVEHPSVTSPLTVEWRA

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 BL21(DE3)

Entity 3 Entity 3 polymer

Description description	Hemagglutinin
Molecular weight formula_weight	1506.8 kDa
Source method src_method	syn
Copy count entity_count	1

Polymer Polymer

Polymer type type	polypeptide(L)
Chain IDs strand_id	C

PKYVKQNTLKLAT

Entity 4 Entity 4 polymer

Description description	extracellular enterotoxin type I
Molecular weight formula_weight	24962.0 kDa
Source method src_method	nat
Copy count entity_count	1

Polymer Polymer

Polymer type type	polypeptide(L)
Chain IDs strand_id	D

QGDIGVGNLRNFYTKHDYIDLKGLIDKNLPSANQLEFSTGINDLISESNNWDEISKFKGKKLDIFGIDYNGPCKSKYMYGGATLSGQYLNSARKIPINLWVNGKHKTISTDKISTNKKLVTAQEIDVKLRRYLQEEYNIYGHNSTGKGKEYGYKSKFYSGFNKGKVLFHLNDEKSFSYDLFYTGDGVPVSFLKIYEDNKIIESEKFHLDVEISYVDSN

Entity 5 Entity 5 non-polymer

Description description	SULFATE ION
Molecular weight formula_weight	96.1 kDa
Source method src_method	syn
Copy count entity_count	4

Entity 6 Entity 6 non-polymer

Description description	4-(2-HYDROXYETHYL)-1-PIPERAZINE ETHANESULFONIC ACID
Molecular weight formula_weight	238.3 kDa
Source method src_method	syn
Copy count entity_count	1

Entity 7 Entity 7 non-polymer

Description description	1,4-DIETHYLENE DIOXIDE
Molecular weight formula_weight	88.1 kDa
Source method src_method	syn
Copy count entity_count	2

Entity 8 Entity 8 non-polymer

Description description	ZINC ION
Molecular weight formula_weight	65.4 kDa
Source method src_method	syn
Copy count entity_count	1

Entity 9 Entity 9 water

Description description	water
Molecular weight formula_weight	18.0 kDa
Source method src_method	nat
Copy count entity_count	460

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6. Fold Classification (SCOP + CATH) 13 domains

SCOP 2.08 (7 domains)

Domain ID domain_id	d2g9ha1
Class class	b — All beta proteins
Fold Fold fold	b.1 — Immunoglobulin-like beta-sandwich
Superfamily Superfamily superfamily	b.1.1 — Immunoglobulin
Family Family family	b.1.1.2 — C1 set domains (antibody constant domain-like)

Domain ID domain_id	d2g9ha2
Class class	d — Alpha and beta proteins (a+b)
Fold Fold fold	d.19 — MHC antigen-recognition domain
Superfamily Superfamily superfamily	d.19.1 — MHC antigen-recognition domain
Family Family family	d.19.1.1 — MHC antigen-recognition domain

Domain ID domain_id	d2g9ha3
Class class	l — Artifacts
Fold Fold fold	l.1 — Tags
Superfamily Superfamily superfamily	l.1.1 — Tags
Family Family family	l.1.1.1 — Tags

Domain ID domain_id	d2g9hb1
Class class	b — All beta proteins
Fold Fold fold	b.1 — Immunoglobulin-like beta-sandwich
Superfamily Superfamily superfamily	b.1.1 — Immunoglobulin
Family Family family	b.1.1.2 — C1 set domains (antibody constant domain-like)

Domain ID domain_id	d2g9hb2
Class class	d — Alpha and beta proteins (a+b)
Fold Fold fold	d.19 — MHC antigen-recognition domain
Superfamily Superfamily superfamily	d.19.1 — MHC antigen-recognition domain
Family Family family	d.19.1.1 — MHC antigen-recognition domain

Domain ID domain_id	d2g9hd1
Class class	b — All beta proteins
Fold Fold fold	b.40 — OB-fold
Superfamily Superfamily superfamily	b.40.2 — Bacterial enterotoxins
Family Family family	b.40.2.2 — Superantigen toxins, N-terminal domain

Domain ID domain_id	d2g9hd2
Class class	d — Alpha and beta proteins (a+b)
Fold Fold fold	d.15 — beta-Grasp (ubiquitin-like)
Superfamily Superfamily superfamily	d.15.6 — Superantigen toxins, C-terminal domain
Family Family family	d.15.6.1 — Superantigen toxins, C-terminal domain

CATH v4.4 (6 domains)

Domain ID domain_id	2g9hA01
Class class	3 — Alpha Beta
Architecture architecture	10 — Roll
Topology topology	320 — Class II Histocompatibility Antigen, M Beta Chain; Chain B, domain 1
Homologous superfamily homologous superfamily	10 — Class II Histocompatibility Antigen, M Beta Chain; Chain B, domain 1

Domain ID domain_id	2g9hA02
Class class	2 — Mainly Beta
Architecture architecture	60 — Sandwich
Topology topology	40 — Immunoglobulin-like
Homologous superfamily homologous superfamily	10 — Immunoglobulins

Domain ID domain_id	2g9hB01
Class class	3 — Alpha Beta
Architecture architecture	10 — Roll
Topology topology	320 — Class II Histocompatibility Antigen, M Beta Chain; Chain B, domain 1
Homologous superfamily homologous superfamily	10 — Class II Histocompatibility Antigen, M Beta Chain; Chain B, domain 1

Domain ID domain_id	2g9hB02
Class class	2 — Mainly Beta
Architecture architecture	60 — Sandwich
Topology topology	40 — Immunoglobulin-like
Homologous superfamily homologous superfamily	10 — Immunoglobulins

Domain ID domain_id	2g9hD01
Class class	3 — Alpha Beta
Architecture architecture	10 — Roll
Topology topology	20 — Ubiquitin-like (UB roll)
Homologous superfamily homologous superfamily	120 —

Domain ID domain_id	2g9hD02
Class class	2 — Mainly Beta
Architecture architecture	40 — Beta Barrel
Topology topology	50 — OB fold (Dihydrolipoamide Acetyltransferase, E2P)
Homologous superfamily homologous superfamily	110 —

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Unit-cell length a length_a	150.395 Å
Unit-cell length b length_b	99.933 Å
Unit-cell length c length_c	72.917 Å
Unit-cell angle α angle_alpha	90.00 °
Unit-cell angle β angle_beta	92.00 °
Unit-cell angle γ angle_gamma	90.00 °
Molecules per unit cell Z z_pdb	4

Space group space_group	C 1 2 1
Space-group number int_tables_number	5
Crystal system crystal_system	—

Resolution resolution	2.000 Å
Low-resolution limit resolution_low	29.790 Å
R factor r_factor	0.2149
R_work r_work	0.2133
R_free r_free	0.2524

Crystal Structure of Staphylococcal Enterotoxin I (SEI) in Complex with a Human MHC class II Molecule

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

HLA class II histocompatibility antigen, DR 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

HLA class II histocompatibility antigen, DRB1-1 beta 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

Hemagglutinin

State in the Current Structure

Other States of the Same Protein in the Database

Monomer

Homodimer

Homotetramer

Other homooligomers

Heteromeric or nucleic-acid complex

extracellular enterotoxin type I

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

2g9h__assembly_1__model_1

2g9h__assembly_1__model_1 | I(q)

2g9h__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 (9)

Entity 1 Entity 1 polymer

Polymer Polymer

Source Source

Entity 2 Entity 2 polymer

Polymer Polymer

Source Source

Entity 3 Entity 3 polymer

Polymer Polymer

Entity 4 Entity 4 polymer

Polymer Polymer

Entity 5 Entity 5 non-polymer

Entity 6 Entity 6 non-polymer

Entity 7 Entity 7 non-polymer

Entity 8 Entity 8 non-polymer

Entity 9 Entity 9 water

6. Fold Classification (SCOP + CATH) 13 domains

SCOP 2.08 (7 domains)

CATH v4.4 (6 domains)

7. Citations (1)