Nucleotide-induced movements in the myosin head near the converter region

Optimization of 3-D hepatocyte culture by controlling the physical and chemical properties of the extra-cellular matrices

Hepatocytes are anchorage-dependent cells sensitive to microenvironment; the control of the physicochemical properties of the extra-cellular matrices may be useful to the maintenance of hepatocyte functions in vitro for various applications. In a microcapsule-based 3-D hepatocyte culture microenvironment, we could control the physical properties of the collagen nano-fibres by fine-tuning the complex-coacervation reaction between methylated collagen and terpolymer of hydroxylethyl methacrylate-methyl methacrylate-methylacrylic acid. The physical properties of the nano-fibres were quantitatively characterized using back-scattering confocal microscopy to help optimize the physical support for hepatocyte functions. We further enhanced the chemical properties of the collagen nano-fibres by incorporating galactose onto collagen, which can specifically interact with the asialoglycoprotein receptor on hepatocytes. By correlating a range of collagen nano-fibres of different physicochemical properties with hepatocyte functions, we have identified a specific combination of methylated and galactosylated collagen nano-fibres optimal for maintaining hepatocyte functions in vitro. A model of how the physical and chemical supports interplay to maintain hepatocyte functions is discussed.

Changes at the interface of the N- and C-terminal parts of the heavy chain of myosin subfragment 1

It has been previously shown that in the M-MgADP-P(i) state, where the myosin head adopts a pre-power stroke conformation, treatment of trypsin-split subfragment 1 of skeletal muscle myosin with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) results in cross-linking of the C-terminal fragment of the heavy chain of S1 -- most probably its converter region -- to the N-terminal S1 heavy-chain fragment, generating a product of 44 kDa [Biochim. Biophys. Acta 1481 (2000) 55]. The results described here show that this product is neither generated in the absence of nucleotide nor in the presence of MgADP or MgPP(i). The 44 kDa cross-linking product can be formed when S1 treated with EDC is complexed with MgADP-AlF(4) or MgADP-V(i) (MgADP-P(i) analogs) and with MgADP-BeF(x), MgATP gamma S or MgAMPPNP (MgATP analogs). The results suggest structural differences between MgATP- or MgADP-P(i)-bound S1, and MgADP-bound or nucleotide-free S1, in spatially close regions of their N- and C-terminal heavy-chain fragments.

Interaction of the N-terminal part of the A1 essential light chain with the myosin heavy chain

The kinetics of actin-dependent MgATPase activity of skeletal muscle myosin subfragment 1 (S1) isoform containing the A1 essential light chain differ from those of the S1 isoform containing the A2 essential light chain. The differences are due to the presence of the extra N-terminal peptide comprising 42 amino acid residues in the A1 light chain. This peptide can interact with actin; heretofore, there have no been reports of the direct interaction between this peptide and the heavy chain of S1. Here, using the zero-length cross-linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and S. aureus V8 protease, we show for the first time that the N-terminal part of the A1-light chain can interact with the 22-kDa fragment of the S1 heavy chain. No such interaction has been observed for the S1(A2) isoenzyme. Localization of residues which can possibly react with the cross-linker suggests that the interaction might involve the N-terminal residues of the A1 light chain and the converter region of the heavy chain.