Cross-linking of the 25- and 20-kilodalton fragments of skeletal myosin subfragment 1 by a bifunctional ATP analogue

Intermolecular cross-linking of a novel rice Kinesin k16 motor domain with a photoreactive ATP derivative

A fluorescent photoreactive ATP derivative, 2'(3')-O-(4-benzoylbenzoyl)-1,N(6)-etheno-ATP (Bz(2)-epsilonATP), was synthesized and reacted with the rice kinesin K16 motor domain (K16MD). In the presence of ADP or ATP, UV irradiation of the K16MD solution containing Bz(2)-epsilonATP resulted in a new 100 kDa band, which was an intermolecular cross-linked product of motor domains. In contrast, no cross-linking was observed in the absence of nucleotides. For the motor domain of mouse brain kinesin and skeletal muscle myosin subfragment-1, no such intermolecular photo cross-linking by Bz(2)-epsilonATP was observed. Our results indicate that Bz(2)-epsilonATP acts unusually as a photoreactive crosslinker to detect conformational changes in K16MD induced by nucleotide binding resulting in the formation of dimers.

Adenine nucleotide binding and photoincorporation in Glanzmann's thrombasthenia platelets

Adenosine 5'-(1-thiotriphosphate) (ATP alpha S) binds to about 25,000 high affinity sites in platelets (Kd approximately 3 nM), competes fully in inhibiting the binding of ADP and, despite the absence of a specific photoactivatable substituent, is directly photoincorporated into a specific 18 kDa domain beginning at Tyr-198 in the alpha chain of glycoprotein IIb (GPIIb alpha) following ultraviolet irradiation of fresh unfixed platelets (Greco et al. (1991) J. Biol. Chem. 266, 13627-13633). 8-azido ATP has now been shown to have similar binding parameters (Kd 8 nM, 20,000 sites/platelet) but, in this case, photoincorporation occurred equally in GPIIb and GPIIIa. To determine the possible function of GPIIb alpha in ADP-induced activation, platelets were isolated from two Glanzmann's thrombasthenia patients whose platelets contain approximately 6% of normal levels of GPIIb. ADP and ATP alpha S bound to intact, formaldehyde-fixed Glanzmann's platelets at high affinity sites with dissociation constants of approximately 30 nM and approximately 2 nM, respectively. Both nucleotides also bound to low affinity sites with dissociation constants of approximately 2 microM: these values are similar to those obtained with control platelets. ATP alpha S antagonized the shape ADP-induced shape change response of Glanzmann's platelets (EC50 5 microM) indicating that it bound to the P2T (ADP) receptor. However, photoincorporation was low (approximately 7% of control) similar to their content of GPIIb alpha. These results show that ADP binding and photoincorporation are occurring at different sites on the platelet surface but suggest that the ADP binding site may be located in proximity to GPIIb alpha.

ATP binding in peptide synthetases: determination of contact sites of the adenine moiety by photoaffinity labeling of tyrocidine synthetase 1 with 2-azidoadenosine triphosphate

Characterization of the nucleotide binding domain in peptide synthetases was approached by photoaffinity labeling of tyrocidine synthetase 1 (TY1) with 2-azidoadenosine triphosphate (2-azido-ATP). Exposure of TY1 in the presence of photolabel to irradiation with ultraviolet light resulted in a time-dependent covalent modification of the enzyme with a concomitant loss of catalytic activity. Inactivation was not observed if incubation was performed in the absence of either light or the nucleotide analogue. Specificity of labeling was indicated by the ability of 2-azido-ATP to serve as a substrate in the amino acid activation reaction. The modified protein was subjected to tryptic digestion, and the fragments labeled by the nucleotide analogue were purified by reverse-phase high-performance liquid chromatography. Sequence analysis identified three tryptic peptides corresponding to residues G373-K384, W405-R416, and L483-K494, derived from the N-terminal half of the TY1 sequence. As this region shows similarity to strongly conserved regions in other peptide synthetases and acyl-CoA synthetases, it is considered to be the region catalyzing aminoacyl adenylate formation. The identified sequences appear to define components of the nucleotide binding domain found in close proximity to the adenine ring in ATP. Conservation of primary structure and homology to other carboxyl-activating enzymes of this superfamily, including peptide synthetases, insect luciferases, and acyl-CoA synthetases, is discussed.

Photoaffinity labelling of smooth-muscle myosin by methylanthraniloyl-8-azido-ATP

Methylanthraniloyl-8-azido-ATP (Mant-8-N3-ATP), which binds to the 20 kDa C-terminal tryptic fragment of skeletal-muscle myosin subfragment-1 [Maruta, Miyanishi and Matsuda (1989) Eur. J. Biochem. 184, 213-221], was synthesized and used as a probe of the conformational change of smooth-muscle myosin. Mant-8-N3-ATP, like ATP, induced the formation of the 10 S conformation at low ionic strength. In the presence of vanadate, smooth-muscle myosin formed a stable complex with Mant-8-N3-ADP, and this complex showed the 10 S-->6 S transition of myosin. ATP-binding sites for 6 S (extended state) and 10 S (folded state) myosin were studied by photolabelling of myosin with Mant-8-N3-ADP. For both 6 S and 10 S myosin, Mant-8-N3-ATP was incorporated into the 29 kDa N-terminal tryptic fragment of myosin heavy chain. This is unlike the labelling of skeletal-muscle myosin, in which the 20 kDa C-terminal fragment is labelled. The labelling of 29 kDa fragment was diminished significantly by addition of ATP. These results suggest that the conformation of the ATP-binding site of smooth-muscle myosin is different from that of skeletal-muscle myosin. To examine further the possible differences in the labelling site between 6 S and 10 S myosin, the affinity-labelled 29 kDa fragment was subjected to complete proteolysis by lysylendo-peptidase. The fluorescent-labelled-peptide map suggested that the Mant-8-N3-ADP-binding sites for 6 S and 10 S myosin were identical.

Molecular movements in the actomyosin complex: F-actin-promoted internal cross-linking of the 25- and 20-kDa heavy chain fragments of skeletal myosin subfragment

We describe, for the first time, the F-actin-promoted changes in the spatial relationship of strands in the NH2-terminal 25-kDa and COOH-terminal 20-kDa heavy chain fragments of the skeletal myosin subfragment 1 (S-1), detected by their exclusive chemical cross-linking in the rigor F-actin-S-1 complex with m-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS). Quantitative electrophoretic analysis of the reaction products showed extensive conversion of the 95-kDa heavy chain of the actin-bound S-1 into a new species with an apparent mass of 135 kDa (yield = 50-60%), whereas the heavy chain mobility remained unaffected when actin was omitted. The 135-kDa entity retained the fluorescence of AEDANS-S-1 but not of AEDANS-actin, indicating that it was not a cross-linked acto-heavy chain adduct. Its extent of production depended markedly on the S-1: actin molar ratio and was maximum near a ratio of 1:4. The MBS treatment of acto-S-1 led also to some covalent actin-actin oligomers which could be suppressed by using trypsin-truncated F-actin lacking Cys-374, without altering the generation of the 135-kDa heavy chain derivative.(ABSTRACT TRUNCATED AT 250 WORDS)