9KP4: Human CASTOR1 in apo form

Crystal structure of human CASTOR1 in apo form. Determined by X-ray diffraction at 3.08 Å resolution. Released 25 Mar 2026.

Method: X-ray diffraction
Resolution: 3.08 Å
Organisms: Escherichia coli (strain K12), Homo sapiens
Chains: 4
Atoms: 18,780
Mol. weight: 309.55 kDa
Released: 25 Mar 2026

Explore 9KP4 in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9KP4 contains 142 α-helices and 151 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: 37 helices, 40 β-strands

Element	Residues	Length	Sheet
β-strand	-368--364	5	1
α-helix	-357--343	15
β-strand	-340--336	5	1
α-helix	-331--322	10
β-strand	-315--311	5	1
α-helix	-307--302	6
β-strand	-298	1	2
α-helix	-297--295	3
α-helix	-291--288	4
β-strand	-285	1	3
α-helix	-283--278	6
β-strand	-276--275	2	4
β-strand	-272--271	2	4
β-strand	-268--263	6	1
β-strand	-260--256	5	5
β-strand	-246	1	6
α-helix	-245--243	3
α-helix	-242--234	9
β-strand	-229--227	3	5
α-helix	-220--213	8
β-strand	-204--203	2	7
β-strand	-198--197	2	7
α-helix	-188--174	15
α-helix	-164--155	10
β-strand	-152--147	6	5
α-helix	-145--143	3
α-helix	-142--136	7
β-strand	-132--129	4	5
α-helix	-128--126	3
β-strand	-125--124	2	6
β-strand	-121--120	2	6
β-strand	-116--115	2	8
β-strand	-114--108	7	1
β-strand	-107	1	2
α-helix	-101--96	6
α-helix	-95--90	6
α-helix	-87--78	10
β-strand	-73--72	2	1
β-strand	-70	1	3
α-helix	-69--63	7
α-helix	-59--48	12
β-strand	-46--45	2	8
α-helix	-44--43	2
α-helix	-38--22	17
α-helix	-17--5	13
α-helix	-4--2	3
β-strand	1-16	16	9
α-helix	17-23	7
α-helix	24-32	9
β-strand	41-46	6	9
β-strand	50-55	6	9
α-helix	57-60	4
β-strand	69-71	3	9
α-helix	75	1
β-strand	76-83	8	9
β-strand	90-91	2	9
α-helix	92-93	2
α-helix	94-97	4
α-helix	98-102	5
α-helix	103-107	5
β-strand	113-116	4	9
β-strand	121-126	6	9
α-helix	127-129	3
α-helix	130-138	9
β-strand	142-147	6	9
β-strand	150-153	4	9
β-strand	178	1	9
β-strand	184-189	6	9
α-helix	194-205	12
β-strand	228-233	6	9
β-strand	236-242	7	9
α-helix	246-248	3
β-strand	263-267	5	9
α-helix	282-290	9
β-strand	296-299	4	9
β-strand	304-309	6	9
α-helix	313-323	11

Chain B: 37 helices, 39 β-strands

Element	Residues	Length	Sheet
α-helix	-372--371	2
β-strand	-367--364	4	10
α-helix	-357--343	15
β-strand	-339--336	4	10
α-helix	-331--322	10
β-strand	-315--311	5	10
α-helix	-310--308	3
α-helix	-307--302	6
β-strand	-298	1	11
α-helix	-297--295	3
α-helix	-291--288	4
β-strand	-285	1	12
α-helix	-282--278	5
β-strand	-276--275	2	13
β-strand	-272--271	2	13
β-strand	-269--263	7	10
β-strand	-260--256	5	14
β-strand	-246	1	15
α-helix	-242--235	8
β-strand	-229--227	3	14
α-helix	-220--218	3
α-helix	-216--213	4
α-helix	-188--174	15
α-helix	-164--156	9
β-strand	-152--147	6	14
α-helix	-145--143	3
β-strand	-132--129	4	14
α-helix	-128--126	3
β-strand	-125	1	15
β-strand	-124	1	16
β-strand	-121	1	16
α-helix	-120--119	2
β-strand	-116--115	2	17
β-strand	-114--108	7	10
β-strand	-107	1	11
α-helix	-101--96	6
α-helix	-95--90	6
α-helix	-87--80	8
β-strand	-73--72	2	10
β-strand	-70	1	12
α-helix	-69--63	7
α-helix	-59--48	12
β-strand	-46--45	2	17
α-helix	-44--43	2
α-helix	-40--38	3
α-helix	-37--23	15
α-helix	-17--5	13
β-strand	3-16	14	18
α-helix	17-19	3
α-helix	24-32	9
β-strand	42-46	5	18
β-strand	50-56	7	18
α-helix	57-60	4
β-strand	69-71	3	18
α-helix	75	1
β-strand	76-81	6	18
α-helix	99-106	8
β-strand	112-116	5	18
β-strand	121-126	6	18
α-helix	130-137	8
β-strand	143	1	18
β-strand	178	1	18
β-strand	184-187	4	18
β-strand	188	1	19
α-helix	198-207	10
β-strand	228-233	6	18
β-strand	236-242	7	18
α-helix	245-248	4
β-strand	254	1	19
β-strand	263-268	6	18
α-helix	281-283	3
α-helix	285-289	5
β-strand	296-299	4	18
β-strand	304-309	6	18
α-helix	313-323	11
α-helix	324-326	3

Chain C: 31 helices, 35 β-strands

Element	Residues	Length	Sheet
β-strand	-367--364	4	20
α-helix	-357--347	11
β-strand	-339--336	4	20
α-helix	-331--321	11
β-strand	-315--311	5	20
α-helix	-310--308	3
α-helix	-307--301	7
β-strand	-298	1	21
α-helix	-291--286	6
β-strand	-285	1	22
α-helix	-283--277	7
β-strand	-276--275	2	23
β-strand	-272--271	2	23
β-strand	-269--263	7	20
β-strand	-260--259	2	24
α-helix	-236--233	4
β-strand	-229--227	3	25
α-helix	-220--217	4
α-helix	-216--214	3
α-helix	-164--158	7
β-strand	-152--150	3	25
β-strand	-148--147	2	24
α-helix	-145--143	3
β-strand	-129	1	24
β-strand	-116--115	2	26
β-strand	-114--108	7	20
β-strand	-107	1	21
α-helix	-101--96	6
α-helix	-95--90	6
α-helix	-87--80	8
β-strand	-73--72	2	20
β-strand	-70	1	22
α-helix	-59--48	12
β-strand	-46--45	2	26
α-helix	-44--43	2
α-helix	-38--25	14
α-helix	-12--9	4
β-strand	2-15	14	27
α-helix	18-23	6
α-helix	24-32	9
α-helix	34-36	3
β-strand	42-46	5	27
β-strand	51-56	6	27
α-helix	57-60	4
β-strand	71	1	27
α-helix	75	1
β-strand	76-82	7	27
α-helix	96-97	2
α-helix	98-102	5
α-helix	103-107	5
β-strand	113-116	4	27
β-strand	121-126	6	27
α-helix	130-137	8
β-strand	144	1	27
β-strand	153	1	27
β-strand	177-178	2	27
β-strand	184-188	5	27
α-helix	191-193	3
α-helix	194-207	14
β-strand	228-233	6	27
β-strand	236-242	7	27
β-strand	263-268	6	27
α-helix	282-285	4
β-strand	296-299	4	27
β-strand	304-309	6	27
α-helix	313-325	13

Chain D: 37 helices, 37 β-strands

Element	Residues	Length	Sheet
β-strand	-368--364	5	28
α-helix	-357--343	15
β-strand	-340--336	5	28
α-helix	-331--322	10
β-strand	-315--311	5	28
α-helix	-310--302	9
β-strand	-298	1	29
α-helix	-291--288	4
β-strand	-285	1	30
α-helix	-283--278	6
β-strand	-276--275	2	31
β-strand	-272--271	2	31
β-strand	-269--263	7	28
β-strand	-260--256	5	32
α-helix	-245--243	3
α-helix	-242--233	10
β-strand	-229--227	3	32
α-helix	-220--213	8
β-strand	-205--203	3	33
β-strand	-198--193	6	33
α-helix	-188--174	15
α-helix	-164--156	9
β-strand	-152--147	6	32
α-helix	-145--143	3
α-helix	-142--136	7
β-strand	-132--129	4	32
α-helix	-128--126	3
α-helix	-124--122	3
α-helix	-120--119	2
β-strand	-116--115	2	34
β-strand	-114--108	7	28
β-strand	-107	1	29
α-helix	-101--96	6
α-helix	-95--90	6
α-helix	-87--78	10
β-strand	-73--72	2	28
β-strand	-70	1	30
α-helix	-69--63	7
α-helix	-59--48	12
β-strand	-46--45	2	34
α-helix	-44--43	2
α-helix	-39--22	18
α-helix	-17--4	14
β-strand	1-15	15	35
α-helix	20-23	4
α-helix	24-32	9
β-strand	41-46	6	35
β-strand	51-56	6	35
α-helix	57-60	4
β-strand	69-71	3	35
β-strand	76-83	8	35
β-strand	91	1	35
α-helix	96-97	2
α-helix	98-102	5
α-helix	103-107	5
β-strand	113-116	4	35
β-strand	121-126	6	35
α-helix	127-129	3
α-helix	130-136	7
β-strand	142-145	4	35
β-strand	152-153	2	35
β-strand	178	1	35
β-strand	184-189	6	35
α-helix	191-193	3
α-helix	194-206	13
β-strand	228-233	6	35
β-strand	236-242	7	35
α-helix	245-248	4
β-strand	263-268	6	35
α-helix	282-290	9
β-strand	296-299	4	35
β-strand	304-309	6	35
α-helix	310-312	3
α-helix	314-322	9

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Maltose/maltodextrin-binding periplasmic protein,Cytosolic arginine sensor for mTORC1 subunit 1	A, B, C, D	protein	704	Escherichia coli (strain K12), Homo sapiens	Q8WTX7 (AlphaFold model)

Sequence of entity 1 (A, B, C, D), FASTA

>9KP4_1 Maltose/maltodextrin-binding periplasmic protein,Cytosolic arginine sensor for mTORC1 subunit 1 (chains A, B, C, D)
MKIEEGKLVIWINGDKGYNGLAEVGKKFEKDTGIKVTVEHPDKLEEKFPQVAATGDGPDI
IFWAHDRFGGYAQSGLLAEITPAAAFQDKLYPFTWDAVRYNGKLIAYPIAVEALSLIYNK
DLLPNPPKTWEEIPALDKELKAKGKSALMFNLQEPYFTWPLIAADGGYAFKYAAGKYDIK
DVGVDNAGAKAGLTFLVDLIKNKHMNADTDYSIAEAAFNKGETAMTINGPWAWSNIDTSA
VNYGVTVLPTFKGQPSKPFVGVLSAGINAASPNKELAKEFLENYLLTDEGLEAVNKDKPL
GAVALKSYEEELAKDPRIAATMENAQKGEIMPNIPQMSAFWYAVRTAVINAASGRQTVDA
ALAAAQTNAVDSAAAMELHILEHRVRVLSVARPGLWLYTHPLIKLLFLPRRSRCKFFSLT
ETPEDYTLMVDEEGFKELPPSEFLQVAEATWLVLNVSSHSGAAVQAAGVTKIARSVIAPL
AEHHVSVLMLSTYQTDFILVREQDLSVVIHTLAQEFDIYREVGGEPVPVTRDDSSNGFPR
TQHGPSPTVHPIQSPQNRFCVLTLDPETLPAIATTLIDVLFYSHSTPKEAASSSPEPSSI
TFFAFSLIEGYISIVMDAETQKKFPSDLLLTSSSGELWRMVRIGGQPLGFDECGIVAQIA
GPLAAADISAYYISTFNFDHALVPEDGIGSVIEVLQRRQEGLAS

Primary citation

CASTOR1 and CASTOR2 respond to different arginine levels to regulate mTORC1 activity. Liu, C., Zhang, Y., Wang, Y. et al. Mol Cell (2026) 86:362-375.e4. DOI 10.1016/j.molcel.2025.12.016 · PubMed

Other PDB entries of the same protein (UniProt Q8WTX7 (AlphaFold model), which also has an AlphaFold model), best resolution first:

9PDO 1.8 Å, Arginine-bound CASTOR1 from Homo sapiens (GATOR2-inspired update)
5I2C 1.8 Å, Arginine-bound CASTOR1 from Homo sapiens
5GT7 2.05 Å, Crystal Structure of Arg-bound CASTOR1
5GV2 2.06 Å, Crystal structure of Arginine-bound CASTOR1 from Homo sapiens
5GS9 2.5 Å, Crystal structure of CASTOR1-arginine
5GT8 2.8 Å, Crystal Structure of apo-CASTOR1
9DX2 3.4 Å, Human GATOR2 complex - CASTOR1 bound state
9LWF 3.41 Å, Cryo-EM structure of dual sensor bound GATOR2 complex
9OTI 3.5 Å, GATOR2 complex bound to arginine sensor CASTOR1
9LVK 3.59 Å, Cryo-EM structure of CASTOR1 bound human GATOR2 complex

Browse structure collections

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