9RFB: Human Rac1

Crystal Structure of Human Rac1 in Complex with the Scaffold Protein POSH (residues 321-348). Determined by X-ray diffraction at 1.85 Å resolution. Released 3 Dec 2025.

Method: X-ray diffraction
Resolution: 1.85 Å
Organism: Homo sapiens
Chains: 4
Atoms: 3,571
Mol. weight: 47.46 kDa
Ligands: PO4, MG, GNP
Released: 3 Dec 2025

Explore 9RFB in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9RFB contains 26 α-helices and 16 β-strands across 4 chains. Residue ranges use author residue numbering, as in the PDB file, from PDBe. To see them in 3D, choose the Cartoon representation with Secondary structure coloring: helices, sheets and coils get different colors.

Chain A: 11 helices, 6 β-strands

Element	Residues	Length	Sheet
β-strand	2-10	9	1
α-helix	16-25	10
β-strand	37-46	10	1
β-strand	49-58	10	1
α-helix	62-64	3
α-helix	68-71	4
β-strand	77-83	7	1
α-helix	87-92	6
α-helix	93-97	5
α-helix	98-104	7
β-strand	110-115	6	1
α-helix	117-119	3
α-helix	123-131	9
α-helix	136-138	3
α-helix	139-148	10
β-strand	153-156	4	1
α-helix	165-176	12

Chain B: 11 helices, 6 β-strands

Element	Residues	Length	Sheet
β-strand	3-10	8	2
α-helix	16-25	10
β-strand	37-46	10	2
β-strand	49-58	10	2
α-helix	62-64	3
α-helix	68-71	4
β-strand	77-83	7	2
α-helix	87-92	6
α-helix	93-97	5
α-helix	98-104	7
β-strand	110-115	6	2
α-helix	117-119	3
α-helix	123-130	8
α-helix	136-138	3
α-helix	139-148	10
β-strand	153-156	4	2
α-helix	165-176	12

Chains C and D: 2 helices, 2 β-strands

Element	Residues	Length	Sheet
β-strand	326	1	1
α-helix	327-329	3
β-strand	330-334	5	1
α-helix	337-340	4

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Ras-related C3 botulinum toxin substrate 1	A, B	protein	180	Homo sapiens	P63000 (AlphaFold model)
E3 ubiquitin-protein ligase SH3RF1	C, D	protein	28	Homo sapiens	Q7Z6J0 (AlphaFold model)

Sequence of entity 1 (A, B), FASTA

>9RFB_1 Ras-related C3 botulinum toxin substrate 1 (chains A, B)
GRRMQAIKCVVVGDGAVGKTCLLISYTTNAFPGEYIPTVFDNYSANVMVDGKPVNLGLWD
TAGQEDYDRLRPLSYPQTDVFLICFSLVSPASFENVRAKWYPEVRHHCPNTPIILVGTKL
DLRDDKDTIEKLKEKKLTPITYPQGLAMAKEIGAVKYLECSALTQRGLKTVFDEAIRAVL

Sequence of entity 2 (C, D), FASTA

>9RFB_2 E3 ubiquitin-protein ligase SH3RF1 (chains C, D)
RHSMEISPPVLISSSNPTAAARISELSG

Ligands and cofactors

ID	Name	Formula	Copies
PO4	Phosphate ion	O4 P	2
MG	Magnesium ion	Mg	2
GNP	Phosphoaminophosphonic acid-guanylate ester	C10 H17 N6 O13 P3	2

Water and common crystallization additives (CL) are not listed.

Primary citation

Hierarchical folding-upon-binding of an intrinsically disordered protein. Kjaer, L.F., Ielasi, F.S., Winbolt, T. et al. Nat Commun (2025) 16:11346-11346. DOI 10.1038/s41467-025-66420-5 · PubMed

Other PDB entries of the same protein (UniProt P63000 (AlphaFold model), which also has an AlphaFold model), best resolution first:

9RFF 1.25 Å, Crystal Structure of Human Rac1 Fused with the Scaffold Protein POSH (residues 319-371)
9IFK 1.34 Å, Crystal structure of Kalirin/Rac1 in complex with DK-2
1MH1 1.38 Å, Small G-protein
9HU8 1.48 Å, Crystal structure of Kalirin/Rac1 in complex with MC-278.
2WKQ 1.6 Å, Structure of a photoactivatable Rac1 containing the Lov2 C450A Mutant
6X1G 1.6 Å, Crystal structure of a GEF domain from the Orientia tsutsugamushi protein OtDUB in…
5O33 1.64 Å, A structure of the GEF Kalirin DH1 domain in complex with the small GTPase Rac1
9IG1 1.65 Å, Crystal structure of Kalirin/Rac1 in complex with DK-652
9I1L 1.68 Å, Crystal structure of Kalirin/Rac1 in complex with RS-009
8I5V 1.73 Å, DOCK10 mutant L1903Y complexed with Rac1
1RYF 1.75 Å, Alternative Splicing of Rac1 Generates Rac1b, a Self-activating GTPase
1RYH 1.75 Å, Alternative Splicing of Rac1 Generates Rac1b, a Self-activating GTPase

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