From there, the vitamin enters the cell interior with the aid of the transport protein CblF, which was discovered by the same research team three years ago. The researchers now show that a second transport protein is actually necessary for this step, thus providing evidence of another cause of hereditary vitamin B12 deficiency.Gene mutation prevents transport of vitamin B12
The gene in question encodes the protein ABCD4, which was previously known as an ABC transporter in other cell organelles, albeit with an insufficiently defined function. It is now clear that it is a vitamin B12 transporter: “We were able to detect ABCD4 in the lysosomes of human skin cells – right next to the already known CblF protein” explains Matthias Baumgartner, a professor of metabolic diseases at Zurich’s University Children’s Hospital. By adding intact ABCD4 protein to the patients’ cells, the researchers were able to rescue the vitamin B12 transport and compensate for the genetic defect. “We also discovered that a targeted change in the ATP binding site of ABCD4 triggered a loss of function,” says Baumgartner. Thus both ABCD4 and CblF proteins are responsible for the transfer of vitamin B12 from the lysosomes into the cell interior, and ATPase activity is involved. Baumgartner concludes: “The results obtained enable the diagnosis and treatment of this hereditary vitamin B12 deficiency.”
This work was funded by the Swiss National Science Foundation (SNF) and by the Canadian Institutes of Health Research and by the Deutsche Forschungsgemeinschaft.Further reading:
Nathalie Huber | Universität Zürich
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