Literature Information

Title	Two new thermostable α-l-rhamnosidases from a novel thermophilic bacterium
Author	Hákon Birgisson, Gudmundur O. Hreggvidsson, Olafur H. Fridjónsson , Andrew Mort, Jakob K. Kristjánsson, Bo Mattiasson
DOI	10.1016/j.enzmictec.2003.12.012
Abstract	Two new thermostable α-l-rhamnosidases with novel substrate hydrolysis pattern were cloned and expressed from a new thermophilic bacterium. Fragments of the two α-l-rhamnosidase genes, rhmA and rhmB were identified in a partially sequenced genome of the bacterium. Whole genes were recovered by amplifying flanking sequences with single specific primers and nonspecific walking primers . The recovered genes were then cloned into Escherichia coli and their enzymes produced and purified. Both enzymes were dimers and the MW of the monomers, were 104 and 107 kDa for RhmA and RhmB, respectively. Both rhamnosidases had a Temperature optimum at 70 °C. RhmA had pH optimum at 7.9 and RhmB had a broad pH optimum of 5.0 to 6.9 and RhmA had over 50% activity in the pH interval 5.0 to 8.7 and RhmB in the pH interval 4.0 to 7.9. Both enzymes had over 20% residual activity after 24-h incubation at 60 °C. RhmA and RhmB had Km values of 0.46 and 0.66 mM and Vmax values of 134 and 352 U mg−1 respectively, on p-nitrophenyl-α-l-rhamnopyranoside. Both rhamnosidases were active on both α-1,2- and α-1,6-linkages tobeta-d-glucoside.

Experimental results

• Enzyme

Uniprot ID: Q6RCI8

Protein: Alpha-L-rhamnosidase

Organism: Thermomicrobia bacterium PRI-1686

Length: 954 AA

Taxonomic identifier: 260956 [NCBI]

• Pfam

Source	Domain	Start	End	E-value (Domain)	Coverage
Pfam-A	Bac_rhamnosid6H	538	873	1.8e-82	0.994

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:

Bac_rhamnosid6H

Pfam

This family consists of bacterial rhamnosidase A and B enzymes. L-Rhamnose is abundant in biomass as a common constituent of glycolipids and glycosides, such as plant pigments, pectic polysaccharides, gums or biosurfactants. Some rhamnosides are important bioactive compounds. For example, terpenyl glycosides, the glycosidic precursor of aromatic terpenoids, act as important flavouring substances in grapes. Other rhamnosides act as cytotoxic rhamnosylated terpenoids, as signal substances in plants or play a role in the antigenicity of pathogenic bacteria¹.

InterPro

The six-hairpin glycoside transferase domain contains up to seven alpha-hairpins arranged in closed circular array. Proteins containing this domain include bacterial rhamnosidase A and B enzymes. L-Rhamnose is abundant in biomass as a common constituent of glycolipids and glycosides, such as plant pigments, pectic polysaccharides, gums or biosurfactants. Some rhamnosides are important bioactive compounds. For example, terpenyl glycosides, the glycosidic precursor of aromatic terpenoids, act as important flavouring substances in grapes. Other rhamnosides act as cytotoxic rhamnosylated terpenoids, as signal substances in plants or play a role in the antigenicity of pathogenic bacteria¹.

Information is taken from Pfam and InterPro web site.

• Reaction

p-nitrophenyl-α-L-rhamnopyranoside + H₂O ⇒ L-rhamnose + p-nitrophenyl

References