Sentence:  Quite what that job is remains obscure, but one theory is that it is to stabilise another protein called <WSD>tau</WSD>, which is supposed in turn to keep in shape the tubular ‘skeleton' of a neuron. 
Meaning of the word marked with <WSD> tags:  Tau protein, a type of protein that stabilizes microtubules in the human central nervous system, failures of which are associated with forms of dementia.