Literature Information

Title	A new monocupin quercetinase of Streptomyces sp. FLA: identification and heterologous expression of the queD gene and activity of the recombinant enzyme towards different flavonols
Author	Hedda Merkens, Sonja Sielker, Karsten Rose & Susanne Fetzner
DOI	10.1007/s00203-007-0215-z
Abstract	The gene queD encoding quercetinase of Streptomyces sp. FLA, a soil isolate related to S. eurythermus T, was identified. Quercetinases catalyze the 2,4-dioxygenolytic cleavage of 3,5,7,3′,4′-pentahydroxyflavone to 2-protocatechuoylphloroglucinol carboxylic acid and carbon monoxide. The queD gene was expressed in S. lividans and E. coli, and the recombinant hexahistidine-tagged protein (QueDHis6) was purified. Several flavonols were converted by QueDHis6, whereas CO formation from the 2,3-dihydroflavonol taxifolin and the flavone luteolin were not observed. In contrast to bicupin quercetinases from Aspergillus japonicus and Bacillus subtilis, and bicupin pirins showing quercetinase activity, QueD of strain FLA is a monocupin exhibiting 35.9% sequence identity to the C-terminal domain of B. subtilis quercetinase. Its native molecular mass of 63 kDa suggests a multimeric protein. A queD-specific probe hybridized with fragments of genomic DNA of four other quercetin degrading Streptomyces strains, but not with DNA of B. subtilis. Potential ORFs upstream of queD probably code for a serine protease and an endoribonuclease; two ORFs downstream of queD may encode an amidohydrolase and a carboxylesterase. This arrangement suggests that queD is not part of a catabolic gene cluster. Quercetinases might play a major role as detoxifying rather thancatabolic enzymes.

Experimental results

• Enzyme

Uniprot ID: A2VA43

Protein: Quercetinase QueD

Organism: Streptomyces sp. FLA

Length: 186 AA

Taxonomic identifier: 375060 [NCBI]

• Pfam

Source	Domain	Start	End	E-value (Domain)	Coverage
Pfam-A	Cupin_2	61	120	1.3e-08	0.761

Program: hmmscan

Version: 3.1b2 (February 2015)

Method: hmmscan --domtblout hmmscan.tbl --noali -E 1e-5 pfam query.fa

Date: Mon Jul 20 14:32:16 2020

Description:

Cupin_2

Pfam

This family represents the conserved barrel domain of the ‘cupin’ superfamily¹ (‘cupa’ is the Latin term for a small barrel).

InterPro

This family represents the conserved barrel domain of the cupin superfamily¹ (cupa is the Latin term for a small barrel).

Information is taken from Pfam and InterPro web site.

• Reaction

quercetin + oxygen ⇒ 2-(3,4-dihydroxybenzoyloxy)-4,6-dihydroxybenzoate + carbon monoxide + H⁺

References