Crystal structure of monomeric actin in the ATP state. Structural basis of nucleotide-dependent actin dynamics.
A nucleotide-dependent conformational change regulates actin filament dynamics. Yet, the structural basis of this mechanism remains controversial. The x-ray crystal structure of tetramethylrhodamine-5-maleimide-actin with bound AMPPNP, a non-hydrolyzable ATP analog, was determined to 1.85-A resolution. A comparison of this structure to that of tetramethylrhodamine-5-maleimide-actin with bound ADP, determined previously under similar conditions, reveals how the release of the nucleotide gamma-phosphate sets in motion a sequence of events leading to a conformational change in subdomain 2. The side chain of Ser-14 in the catalytic site rotates upon Pi release, triggering the rearrangement of the loop containing the methylated His-73, referred to as the sensor loop. This in turn causes a transition in the DNase I-binding loop in subdomain 2 from a disordered loop in ATP-actin to an ordered alpha-helix in ADP-actin. Despite this conformational change, the nucleotide cleft remains closed in ADP-actin, similar to ATP-actin. An analysis of the existing structures of members of the actin superfamily suggests that the cleft is open in the nucleotide-free state.
Graceffa
Philip
P
Boston Biomedical Research Institute, Watertown, Massachusetts 02472, USA.
Dominguez
Roberto
R
D000199:Actins / Q000737:chemistry*; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000266:Adenylyl Imidodiphosphate / Q000737:chemistry; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003850:Deoxyribonuclease I / Q000737:chemistry; D003851:Deoxyribonucleases / Q000737:chemistry; D005456:Fluorescent Dyes / Q000494:pharmacology; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D009711:Nucleotides / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012235:Rhodamines / Q000494:pharmacology; D012694:Serine / Q000737:chemistry
D000199:Actins; D005456:Fluorescent Dyes; D009711:Nucleotides; D010710:Phosphates; D012235:Rhodamines; D000266:Adenylyl Imidodiphosphate; D012694:Serine; D006639:Histidine; C005358:tetramethylrhodamine; D000255:Adenosine Triphosphate; D003851:Deoxyribonucleases; D003850:Deoxyribonuclease I