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General model of myosin filament structure. III Molecular packing arrangements in myosin filaments
J. Mol. Biol. (1974) 84, 374
Errata General Model of Myosin Filament Structure. III Molecular Packing Arrangements in Myosin Filaments J. M.
SQUIRE
J. Mol. Biol. (1973) 77, 291-323 (1) Page 317,13 lines from the bottom of the page the sentence should read: Evidence of a thick filament repeat longer than 720 B (about 4 x 720 8) in the anterior byssus retractor muscle of Mytilus (a = 550 to 600 8; Squire, 1971) has been obtained. . . . (2) Page 318, 13 lines from the bottom of the page delete paragraph from “Pepe’s model is based on . . . ” and insert instead: Pepe’s model is based on the assumption that there are 6n myosin molecules (n integral) in a repeat of 430 A of the myosin filaments. However, as mentioned earlier, biochemical and theoretical studies of myosin 6lament structure (Squire, 1971,1972; Tregear & Squire, 1973) have now shown that, on present evidence, the most likely symmetry of the myosin filaments in vertebrate striated muscle is that of a threestranded helix of pitch 1296 L! containing nine molecules in the 430 L%repeat. This is clearly incompatible with the assumption on which Pepe’s model is based. It should be noted that the original statement that “Pepe’s model is based on the assumption that the symmetry of these filaments is that proposed by Huxley & Brown (1967) . . .” is factually incorrect. Pepe made his own deductions about the likely symmetry of these filaments independently of Huxley & Brown (1967). I would like to apologise for this error. (3) Page 318,4 lines from the bottom of the page comment (i) should have been more clear a,nd is open to misinterpretation. It should have read: The type of lateral packing arrangement between myosin molecules in Pepe’s model is hexagonal throughout, which is supported Pepe claims by the observations of Pepe & Drucker (1972, J. Cell. Biol. 52, 255260). On the other hand it seems for reasons given earlier that such 2-strand a-helical molecules tend to pack in quasitetragonal arrangements (see also Caspar et al., 1969; Elliott et al., 1968a). Note that in the general model some quasi-tetragonal packing is maintained despite the necessity for the packing to tend to an arrangement with 3-fold symmetry towards the centre of the three-stranded cylindrical filament. (4) Page 319, 8 lines from the top of the page comment (v) was based on Pepe’s publications up to the time of writing and his existing model did not include antiparallel overlaps between adjacent molecules of about 900 A and about 1300 A (see for example Pig. 12 in : Pepe, I?. A. (1973). Cold Spring Harbor Symp. &ant. Biol. 37, 97-108). However, in a recent personal communication Pepe states that these overlaps can be generated by adding to his existing model a number of extra myosin molecules placed in the appropriate positions on the surface of the bare-zone region of the model. 374
Errata General Model of Myosin Filament Structure. III Molecular Packing Arrangements in Myosin Filaments J. M.
SQUIRE
J. Mol. Biol. (1973) 77, 291-323 (1) Page 317,13 lines from the bottom of the page the sentence should read: Evidence of a thick filament repeat longer than 720 B (about 4 x 720 8) in the anterior byssus retractor muscle of Mytilus (a = 550 to 600 8; Squire, 1971) has been obtained. . . . (2) Page 318, 13 lines from the bottom of the page delete paragraph from “Pepe’s model is based on . . . ” and insert instead: Pepe’s model is based on the assumption that there are 6n myosin molecules (n integral) in a repeat of 430 A of the myosin filaments. However, as mentioned earlier, biochemical and theoretical studies of myosin 6lament structure (Squire, 1971,1972; Tregear & Squire, 1973) have now shown that, on present evidence, the most likely symmetry of the myosin filaments in vertebrate striated muscle is that of a threestranded helix of pitch 1296 L! containing nine molecules in the 430 L%repeat. This is clearly incompatible with the assumption on which Pepe’s model is based. It should be noted that the original statement that “Pepe’s model is based on the assumption that the symmetry of these filaments is that proposed by Huxley & Brown (1967) . . .” is factually incorrect. Pepe made his own deductions about the likely symmetry of these filaments independently of Huxley & Brown (1967). I would like to apologise for this error. (3) Page 318,4 lines from the bottom of the page comment (i) should have been more clear a,nd is open to misinterpretation. It should have read: The type of lateral packing arrangement between myosin molecules in Pepe’s model is hexagonal throughout, which is supported Pepe claims by the observations of Pepe & Drucker (1972, J. Cell. Biol. 52, 255260). On the other hand it seems for reasons given earlier that such 2-strand a-helical molecules tend to pack in quasitetragonal arrangements (see also Caspar et al., 1969; Elliott et al., 1968a). Note that in the general model some quasi-tetragonal packing is maintained despite the necessity for the packing to tend to an arrangement with 3-fold symmetry towards the centre of the three-stranded cylindrical filament. (4) Page 319, 8 lines from the top of the page comment (v) was based on Pepe’s publications up to the time of writing and his existing model did not include antiparallel overlaps between adjacent molecules of about 900 A and about 1300 A (see for example Pig. 12 in : Pepe, I?. A. (1973). Cold Spring Harbor Symp. &ant. Biol. 37, 97-108). However, in a recent personal communication Pepe states that these overlaps can be generated by adding to his existing model a number of extra myosin molecules placed in the appropriate positions on the surface of the bare-zone region of the model. 374