A transport protein that’s utilized by the human pathogen Mycobacterium tuberculosis to import vitamin B12 seems to be very totally different from different transport proteins. It comprises an enormous water-crammed cavity, through which hydrophilic substances are transported throughout the cell membrane. This discovery, which adjustments our understanding of bacterial physiology, was made by imaging the transport protein utilizing cryo-electron microscopy. The results had been revealed within the journal Nature on 26 March.
The tuberculosis bacterium has all of the genes required to supply vitamin B12; however, for some cause, it nonetheless must import this vitamin for profitable cell division. To take action, it makes use of a transport protein that’s half of a giant household of ATP-binding cassette (ABC) transporters. Curiously, the vitamin B12 transporter can be implicated within the transport of antimicrobial peptides corresponding to bleomycin. ‘And it is rather odd to have a single transporter for two very various kinds of molecules,’ says Professor of Biochemistry Dirk Slotboom.
Slotboom and his crew, along with their colleague Albert Guskov, got down to elucidate the protein construction of the enigmatic transporter. ‘This was a protracted course of however we lastly cracked it utilizing cryo-electron microscopy,’ says Slotboom. This was carried out on the SLAC Nationwide Accelerator Laboratory, Menlo Park, CA, USA. The construction revealed a serious shock: a water-crammed cavity that spans your entire cell membrane, measuring an enormous 7,700 cubic Angstrom. ‘That’s as massive as seven vitamin B12 molecules.’
This cavity seems to easily transport water along with any substances that could be in it. ‘You possibly can evaluate it with a sluice,’ explains Slotboom. ‘You let the water in and all the things that are in it.’ It does clarify why the transporter can deal with each antibiotic peptides and vitamin B12. Since it’s non-selective, it has to be an inefficient transport system. This doesn’t matter for the uptake of vitamin B12 by Mycobacterium tuberculosis, because the cells solely must take up only a few of those molecules throughout their reproductive cycle, which lasts around 24 hours.