How to proteins move along DNA? Lessons from type-I and type-III restriction endonucleases.
Protein-mediated communications on DNA are universally important. The translocation of DNA driven by a high-energy phosphoryl potential allows long stretches of DNA to be traversed without dissociation. Type-I and type-III enzymes both use a common DNA-tracking mechanism to move along DNA, dependent on the hydrolysis of ATP. Type-I enzymes cleave DNA at distant DNA sites (and in some cases close to the site), due to a stall in enzyme motion. This can be due to collision with another translocating type-I enzyme or, on circular DNA, due to an increased topological load. ATP hydrolysis is considerable, and continues after DNA cleavage. Type-III enzymes only cleave DNA proximal to their sites due to collision between two endonucleases tracking with defined polarity. ATP hydrolysis is less than with the type-I enzymes. Homology to DNA helicases has been found within the HsdR and Res subunits. Mutagenesis of the DEAD-box motifs affects both ATP hydrolysis and DNA cleavage. This demonstrates a tight link between ATPase and endonuclease activities. A strand-separation mechanism akin to the DNA helicases is a possibility. The DNA-based motor proteins are mechanistically ill-defined. Further study using some of the techniques pioneered with classical motor proteins will be needed to reveal more detail.
Szczelkun
M D
MD
Department of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K.
D000818:Animals; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D015253:Deoxyribonucleases, Type I Site-Specific / Q000378:metabolism*; D015263:Deoxyribonucleases, Type III Site-Specific / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D021381:Protein Transport / Q000502:physiology*
D004268:DNA-Binding Proteins; D004247:DNA; D015253:Deoxyribonucleases, Type I Site-Specific; D015263:Deoxyribonucleases, Type III Site-Specific