Tài liệu Báo cáo khoa học: Looking for the ancestry of the heavy-chain subunits of heteromeric amino

Looking for the ancestry of the heavy-chain subunits of

heteromeric amino acid transporters rBAT and 4F2hc

within the GH13 a-amylase family

Marek Gabrisˇko1 and Sˇ tefan Janecˇek1,2

1 Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovakia

2 Department of Biotechnology, Faculty of Natural Sciences, University of SS. Cyril and Methodius, Trnava, Slovakia

Introduction

To fulfil its metabolic needs, a cell uses specialized

transport proteins to perform and control the uptake

and efflux of crucial compounds (e.g. sugars, amino

acids, nucleotides, inorganic ions and drugs) across

the plasma membrane. These proteins have been clas￾sified into the phylogenetically derived solute carrier

(SLC) families; current classification counts almost 50

SLC families [1,2]. The sequence similarity between

the heavy-chain subunits of heteromeric amino acid

transporters (hcHATs) and the a-glucosidases from

the a-amylase family [3] was first recognized more

than 15 years ago [4]. HATs are composed proteins

consisting of a light subunit (SLC7 members) and a

heavy subunit (known as rBAT or 4F2hc; SLC3

Keywords

4F2hc; evolutionary relatedness; oligo-1,6-

glucosidase subfamily; rBAT; a-amylase

family

Correspondence

Sˇ . Janecˇek, Institute of Molecular Biology,

Slovak Academy of Sciences, Du´bravska´

cesta 21, SK-84551 Bratislava, Slovakia

Fax: +421 2 59307416

Tel: +421 2 59307420

E-mail: [email protected]

(Received 15 July 2009, revised

18 September 2009, accepted 12 October

2009)

doi:10.1111/j.1742-4658.2009.07434.x

In an effort to shed more light on the early evolutionary history of the

heavy-chain subunits of heteromeric amino acid transporters (hcHATs)

rBAT and 4F2hc within the a-amylase family GH13, a bioinformatics

study was undertaken. The focus of the study was on a detailed sequence

comparison of rBAT and 4F2hc proteins from as wide as possible taxo￾nomic spectrum and enzyme specificities from the a-amylase family. The

GH13 enzymes were selected from the so-called GH13 oligo-1,6-glucosidase

and neopullulanase subfamilies that represent the a-amylase family enzyme

groups most closely related to hcHATs. Within this study, more than 30

hcHAT-like proteins, designated here as hcHAT1 and hcHAT2 groups,

were identified in basal Metazoa. Of the GH13 catalytic triad, only the cat￾alytic nucleophile (aspartic acid 199 of the oligo-1,6-glucosidase) could

have its counterpart in some 4F2hc proteins, whereas most rBATs contain

the correspondences for the entire GH13 catalytic triad. Moreover, the

4F2hc proteins lack not only domain B typical for GH13 enzymes, but also

a stretch of 40 amino acid residues succeeding the b4-strand of the cata￾lytic TIM barrel. rBATs have the entire domain B as well as longer loop 4.

The higher sequence–structural similarity between rBATs and GH13

enzymes was reflected in the evolutionary tree. At present it is necessary to

consider two different scenarios on how the chordate rBAT and 4F2hc

proteins might have evolved. The GH13-like protein from the cnidarian

Nematostella vectensis might nowadays represent a protein close to the

eventual ancestor of the hcHAT proteins within the GH13 family.

Abbreviations

ATG, amino acid transporter glycoprotein; CSR, conserved sequence regions; GH, glycoside hydrolase; HAT, heteromeric amino acid

transporter; hcHAT, heavy-chain subunits of heteromeric amino acid transporter; SLC, solute carrier.

FEBS Journal 276 (2009) 7265–7278 ª 2009 The Authors Journal compilation ª 2009 FEBS 7265