Reviewed, UniProtKB/Swiss-Prot P28012 (CFI1_MEDSA)

Names and origin

Protein names

Recommended name:
    Chalcone--flavonone isomerase 1
      Short name=Chalcone isomerase 1
    EC=5.5.1.6

Gene names

Name:	CHI1
Synonyms:	CHI-1

Organism

Medicago sativa (Alfalfa)

Taxonomic identifier

3879 [NCBI]

Taxonomic lineage

Eukaryota › Viridiplantae › Streptophyta › Embryophyta › Tracheophyta › Spermatophyta › Magnoliophyta › eudicotyledons › core eudicotyledons › rosids › eurosids I › Fabales › Fabaceae › Papilionoideae › Trifolieae › Medicago

Protein attributes

Sequence length	222 AA.
Sequence status	Complete.
Sequence processing	The displayed sequence is not processed.
Protein existence	Evidence at protein level.

General annotation (Comments)

Function	Catalyzes the intramolecular cyclization of bicyclic chalcones into tricyclic (S)-flavanones. Responsible for the isomerization of 4,2',4',6'-tetrahydroxychalcone (also termed chalcone) into naringenin. Ref.3 Ref.4 Ref.5
Catalytic activity	A chalcone = a flavanone.
Pathway	Secondary metabolite biosynthesis; flavonoid biosynthesis.
Developmental stage	Highest expression in young root tips.
Miscellaneous	Part of the biosynthetic pathway for all classes of flavonoids, a large class of secondary plant metabolites, many of which are brightly colored.
Sequence similarities	Belongs to the chalcone isomerase family.
biophysicochemical properties	Kinetic parameters: KM=8.4 µM for 4,2',4'-trihydroxychalcone (at pH 7.5 and 25 degrees Celsius) KM=15.7 µM for 6'-deoxychalcone (at pH 7.5 and 25 degrees Celsius) KM=22.7 µM for 2',4'-dihydroxychalcone (at pH 7.5 and 25 degrees Celsius) KM=42.5 µM for 4,2'-dihydroxychalcone (at pH 7.5 and 25 degrees Celsius) KM=112 µM for 4,2',4',6'-tetrahydroxychalcone (at pH 7.5 and 25 degrees Celsius) pH dependence: Optimum pH is 7-8.5 with 4,2',4'-trihydroxychalcone as substrate, at 25 degrees Celsius.

Ontologies

Keywords
Biological process	Flavonoid biosynthesis
Molecular function	Isomerase
Technical term	3D-structure
Gene Ontology (GO)
Biological process	flavonoid biosynthetic process Inferred from electronic annotation. Source: UniProtKB-KW
Molecular function	chalcone isomerase activity Inferred from electronic annotation. Source: EC
Complete GO annotation...

Sequence annotation (Features)

Feature key

Position(s)

Length

Description

Graphical view

Feature identifier

Molecule processing

Chain

1 – 222

222

Chalcone--flavonone isomerase 1

PRO_0000166434

Sites

Binding site

48

1

Substrate By similarity

Binding site

113

1

Substrate By similarity

Binding site

190

1

Substrate By similarity

Site

106

1

Important for catalytic activity

Experimental info

Mutagenesis

48

1

T → A: Strongly reduced reaction rate. Ref.4

Mutagenesis

48

1

T → S: Reduced reaction rate. Ref.4

Mutagenesis

106

1

Y → F: Strongly reduced reaction rate. Ref.3 Ref.4

Mutagenesis

113

1

N → A: Reduced reaction rate. Ref.4

Mutagenesis

190

1

T → A: Reduced reaction rate. Ref.4

Secondary structure

1

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222

Helix Strand Turn

Details...

Beta strand

8 – 10

3

Beta strand

13 – 15

3

Beta strand

17 – 20

4

Turn

22 – 24

3

Beta strand

27 – 40

14

Beta strand

43 – 55

13

Helix

58 – 66

9

Helix

71 – 75

5

Helix

78 – 86

9

Beta strand

91 – 99

9

Helix

103 – 120

18

Helix

126 – 139

14

Beta strand

149 – 155

7

Turn

156 – 158

3

Beta strand

159 – 169

11

Beta strand

175 – 179

5

Helix

181 – 192

12

Helix

200 – 214

15

Sequences

	Sequence		Length	Mass (Da)
	P28012-1 [UniParc]. Last modified August 1, 1992. Version 1. Checksum: 7767A72084AB4800	FASTA	222	23,826
	10 20 30 40 50 60 MAASITAITV ENLEYPAVVT SPVTGKSYFL GGAGERGLTI EGNFIKFTAI GVYLEDIAVA 70 80 90 100 110 120 SLAAKWKGKS SEELLETLDF YRDIISGPFE KLIRGSKIRE LSGPEYSRKV MENCVAHLKS 130 140 150 160 170 180 VGTYGDAEAE AMQKFAEAFK PVNFPPGASV FYRQSPDGIL GLSFSPDTSI PEKEAALIEN 190 200 210 220 KAVSSAVLET MIGEHAVSPD LKRCLAARLP ALLNEGAFKI GN

References

[1]	"Isolation of chalcone synthase and chalcone isomerase cDNAs from alfalfa (Medicago sativa L.): highest transcript levels occur in young roots and root tips." McKhann H.I., Hirsch A.M. Plant Mol. Biol. 24:767-777(1994) [PubMed: 8193301] [Abstract] Cited for: NUCLEOTIDE SEQUENCE [MRNA]. Strain: cv. Iroquois.
[2]	Erratum McKhann H.I., Hirsch A.M. Plant Mol. Biol. 25:759-759(1994)
[3]	"Structure and mechanism of the evolutionarily unique plant enzyme chalcone isomerase." Jez J.M., Bowman M.E., Dixon R.A., Noel J.P. Nat. Struct. Biol. 7:786-791(2000) [PubMed: 10966651] [Abstract] Cited for: X-RAY CRYSTALLOGRAPHY (1.85 ANGSTROMS) IN COMPLEX WITH (2S)-NARINGENIN, FUNCTION, BIOPHYSICOCHEMICAL PROPERTIES, MUTAGENESIS OF TYR-106.
[4]	"Role of hydrogen bonds in the reaction mechanism of chalcone isomerase." Jez J.M., Bowman M.E., Noel J.P. Biochemistry 41:5168-5176(2002) [PubMed: 11955065] [Abstract] Cited for: X-RAY CRYSTALLOGRAPHY (2.3 ANGSTROMS), FUNCTION, BIOPHYSICOCHEMICAL PROPERTIES, MUTAGENESIS OF THR-48; TYR-106; ASN-113 AND THR-190.
[5]	"Reaction mechanism of chalcone isomerase. pH dependence, diffusion control, and product binding differences." Jez J.M., Noel J.P. J. Biol. Chem. 277:1361-1369(2002) [PubMed: 11698411] [Abstract] Cited for: X-RAY CRYSTALLOGRAPHY (2.1 ANGSTROMS), FUNCTION, BIOPHYSICOCHEMICAL PROPERTIES.

Cross-references

Sequence databases

EMBLGenBankDDBJ

M91079 mRNA. Translation: AAB41524.1.

PIR

S44371.

3D structure databases

PDBPDBe

Entry	Method	Resolution (Å)	Chain	Positions	PDBsum
1EYP	X-ray	2.50	A/B	1-222	[»]
1EYQ	X-ray	1.85	A/B	1-222	[»]
1FM7	X-ray	2.30	A/B	1-222	[»]
1FM8	X-ray	2.30	A/B	1-222	[»]
1JEP	X-ray	2.10	A/B	1-222	[»]
1JX0	X-ray	2.85	A/B	1-222	[»]
1JX1	X-ray	2.30	A/B/C/D/E/F	1-222	[»]

ModBase

Search...

Enzyme and pathway databases

BRENDA

5.5.1.6. 815.

Family and domain databases

InterPro

IPR016088. Chalcone_isomerase_3-sand.
IPR003466. Chalcone_isomerase_subgr.
[Graphical view]

Gene3D

G3DSA:3.50.70.10. Chalcone. 1 hit.

Pfam

PF02431. Chalcone. 1 hit.
[Graphical view]

ProtoNet

Search...

Entry information

Entry name

CFI1_MEDSA

Accession

Primary (citable) accession number: P28012

Entry history

Integrated into UniProtKB/Swiss-Prot:	August 1, 1992
Last sequence update:	August 1, 1992
Last modified:	June 16, 2009
This is version 56 of the entry and version 1 of the sequence. [Complete history]

Entry status

Reviewed (UniProtKB/Swiss-Prot)

Annotation project

PPAP (Plant Proteome Annotation Project)