Protein mannosylation in actinobacteria an enigmatic post-translational modification

Protein glycosylation is a very common post-translational modification seen in all branches of biology. The functional roles for protein glycosylation are many and varied, essential in eukaryotes but seemingly dispensable in bacteria. One group of bacteria where protein glycosylation has been looked at for at least 50 years are the actinobacteria, a large and diverse group of bacteria which include well know pathogens like Mycobacteria tuberculosis, Corynebacterium diphtheriae, and well know species important in biotechnology like Streptomyces lividans and Corynebacterium glutamicum. Actinobacterial protein glycosylation is a form of protein O-mannosylation which is found widely in eukaryotes from single celled yeast to complex multicellular organisms but is much less understood at the functional level. Very few direct roles for protein O-mannosylation have been described in the literature. This review examines newer findings from the actinobacterial research literature which with the help of glycoprotein models suggests how the glycans might play a role in actinobacterial growth and physiology.