PROTOFILAMENT AS A STRUCTURAL ELEMENT OF FLAGELLA OF HALOALKALOPHILICARCHAEBACTERIA

Flagella of the haloalkalophilic archaebacterium Natronobacterium maga dii were purified and characterized. The diameter of the flagella was 10 nm. It was shown that the flagella consist of four major proteins w ith molecular weights of 105 000, 60 000, 59 000, and 45 000. With dec reasing NaCl concentration, the flagella dissociated into protofilamen ts. The structure of dissociated flagella and individual flagellins wa s studied by limited proteolysis. It was found that proteolytic cleava ge of flagellins in dissociated flagella into high molecular weight fr agments (about 40 000) did not lead to protofilament degradation. It w as shown that the most stable fragment is formed from the 60 000 molec ular weight flagellin. Cleavage of this fragment led to complete disap pearance of protofilaments. On the basis of the data obtained, possibl e principles of archaebacterial flagellar construction are discussed.