Membrane Topological Model of Glycosyltransferases of the GT-C Superfamily.

Andreia Albuquerque-Wendt,Françoise H Routier,Falk F R Buettner,Hermann J Hütte,Hans Bakker

doi:10.3390/ijms20194842

Andreia Albuquerque-Wendt, Françoise H Routier + Show 3 more

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https://doi.org/10.3390/ijms20194842

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Abstract

Glycosyltransferases that use polyisoprenol-linked donor substrates are categorized in the GT-C superfamily. In eukaryotes, they act in the endoplasmic reticulum (ER) lumen and are involved in N-glycosylation, glypiation, O-mannosylation, and C-mannosylation of proteins. We generated a membrane topology model of C-mannosyltransferases (DPY19 family) that concurred perfectly with the 13 transmembrane domains (TMDs) observed in oligosaccharyltransferases (STT3 family) structures. A multiple alignment of family members from diverse organisms highlighted the presence of only a few conserved amino acids between DPY19s and STT3s. Most of these residues were shown to be essential for DPY19 function and are positioned in luminal loops that showed high conservation within the DPY19 family. Multiple alignments of other eukaryotic GT-C families underlined the presence of similar conserved motifs in luminal loops, in all enzymes of the superfamily. Most GT-C enzymes are proposed to have an uneven number of TDMs with 11 (POMT, TMTC, ALG9, ALG12, PIGB, PIGV, and PIGZ) or 13 (DPY19, STT3, and ALG10) membrane-spanning helices. In contrast, PIGM, ALG3, ALG6, and ALG8 have 12 or 14 TMDs and display a C-terminal dilysine ER-retrieval motif oriented towards the cytoplasm. We propose that all members of the GT-C superfamily are evolutionary related enzymes with preserved membrane topology.

Highlights

Glycosyltransferases may be classified and named according to the reaction that they catalyze and their substrate specificity
Enzymes of different species often show distinct patterns of transmembrane domains (TMDs) probability. To partly overcome this variation, we used the program PolyPhobius [25]. This algorithm can be supplied with a multiple sequence alignment and predicts TMDs of the first sequence in the alignment but bases the prediction on the multiple sequence alignment
Annotation of the membrane-spanning domains of DPY19L1 was based on comparison with STT3A and corresponds to the 13 domains previously predicted for the C. elegans enzyme [8]

Summary

Introduction

Glycosyltransferases may be classified and named according to the reaction that they catalyze and their substrate specificity. A classification based on sequence similarities has been adopted and currently organizes glycosyltransferases in 106 distinct CAZy (Carbohydrate Active enZYmes) GT families (http://www.cazy.org/GlycosylTransferases.html) [1]. The majority of these enzymes use nucleotide sugars as donor substrates, whereas others require a polyisoprenoid lipid carrier for presentation of the monosaccharide or oligosaccharide. The glycosyltransferases that use dolichol-phosphate (Dol-P)- or dolichol-diphosphate (Dol-PP)-linked substrates act in the endoplasmic reticulum (ER) and are involved in N-glycosylation, glypiation, O-mannosylation, and C-mannosylation of proteins (Figure 1).

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