Peptide maps of the myosin isoenzymes of Acanthamoeba castellanii.

Extracts of Acanthamoeba castellanii contain four myosin-like ATPases (Maruta, H., Gadasi, H., Collins, J.H., and Korn, E.D. (1979) J. Biol. Chem. 254, 3624-3630): double-headed Acanthamoeba myosin II and single-headed Acanthamoeba myosins IA, IB, and IC, which have heavy chains of 170,000, 130,000, 125,000, and 130,000 daltons, respectively, as well as different light chains. In the accompanying paper, evidence is presented that suggests that Acanthamoeba myosin IC is the same molecule as Acanthamoeba myosin IA plus a regulatory 20,000-dalton peptide. This conclusion is confirmed by the identity of the peptide maps obtained by limited proteolysis of the heavy chains of Acanthamoeba myosins IA and IC by Staphylococcus aureus V8 protease. However, peptide maps of the heavy chains of Acanthamoeba myosins IA, IB, and II obtained by limited proteolysis by the Staphylococcus protease and chymotrypsin and by chemical cleavage by cyanogen bromide and cyanylation have few, if any, peptides in common. From this evidence, and the enzymatic and subunit data in the accompanying paper, it is concluded that the three Acanthamoeba myosin isoenzymes, IA (IC), IB, and II, are products of different genes.     

Preparation, crystal structure and properties of a novel microporous Cu coordination polymer with 6-quinolinecarboxylate

A microporous coordination polymer formulated as {[Cu(L)₂] · (DMF)₂}_n (1) has been prepared by the direct reaction of copper nitrate with 6-quinolinecarboxylic acid (HL) in DMF. X-ray single crystal diffraction of 1 reveals that the [Cu₂(COO)₄] secondary building units are interconnected by the bridging L ligands to generate a layered framework with the terminal L ligands as lateral pendants at both sides. Furthermore, the unusual inserted integration of the coordination layers, regulated and fixed by interlayer aromatic stacking interactions between the terminal ligands, leads to the formation of a novel 3-D microporous crystalline lattice with different 1-D channels along three directions. The gas adsorption and magnetic character of this crystalline material have also been investigated.     

Characterization of a novel rice kinesin O12 with a calponin homology domain

Genomic analysis predicted that the rice (Oryza sativa var. japonica) genome encodes at least 41 kinesin-like proteins including the novel kinesin O12, which is classified as a kinesin-14 family member. O12 has a calponin homology (CH) domain that is known as an actin-binding domain. In this study, we expressed the functional domains of O12 in Escherichia coli and determined its enzymatic characteristics compared with other kinesins. The microtubule-dependent ATPase activity of recombinant O12 containing the motor and CH domains was significantly reduced in the presence of actin. Interestingly, microtubule-dependent ATPase activity of the motor domain was also affected by actin in the absence of the CH domain. Our findings suggest that the motor activity of the rice plant-specific kinesin O12 may be regulated by actin.     

Translocation and the alternative D-galacturonate pathway contribute to increasing the ascorbate level in ripening tomato fruits together with the D-mannose/L-galactose pathway

The D-mannose/L-galactose pathway for the biosynthesis of vitamin C (L-ascorbic acid; AsA) has greatly improved the understanding of this indispensable compound in plants, where it plays multifunctional roles. However, it is yet to be proven whether the same pathway holds for all the different organs of plants, especially the fruit-bearing plants, at different stages of development. Micro-Tom was used here to elucidate the mechanisms of AsA accumulation and regulation in tomato fruits. The mRNA expression of the genes in the D-mannose/L-galactose pathway were inversely correlated with increasing AsA content of Micro-Tom fruits during ripening. Feeding L-[6-(14)C]AsA to Micro-Tom plants revealed that the bulk of the label from AsA accumulated in the source leaf was transported to the immature green fruits, and the rate of translocation decreased as ripening progressed. L-Galactose feeding, but neither D-galacturonate nor L-gulono-1,4-lactone, enhanced the content of AsA in immature green fruit. On the other hand, L-galactose and D-galacturonate, but not L-gulono-1,4-lactone, resulted in an increase in the AsA content of red ripened fruits. Crude extract prepared from insoluble fractions of green and red fruits showed D-galacturonate reductase- and aldonolactonase-specific activities, the antepenultimate and penultimate enzymes, respectively, in the D-galacturonate pathway, in both fruits. Taken together, the present findings demonstrated that tomato fruits could switch between different sources for AsA supply depending on their ripening stages. The translocation from source leaves and biosynthesis via the D-mannose/L-galactose pathway are dominant sources in immature fruits, while the alternative D-galacturonate pathway contributes to AsA accumulation in ripened Micro-Tom fruits.     

Constitutive cleavage of the single-pass transmembrane protein alcadeinα prevents aberrant peripheral retention of Kinesin-1

Various membrane proteins are shed by proteinases, constitutively and/or when stimulated by external signals. While the physiological significance of external signal-induced cleavages has been intensely investigated, relatively little is known about the function of constitutive cleavages. Alcadeinα (Alcα; also called Calsyntenin-1) is an evolutionarily conserved type I single-pass transmembrane protein that binds to kinesin-1 light chain (KLC) to activate kinesin-1's transport of Alcα-containing vesicles. We found that Alcα was constitutively and efficiently cleaved to liberate its ectodomain into the extracellular space, and that full-length Alcα protein was rarely detected on the cell surface. The secretion efficiency of the ectodomain was unaltered by a mutation that both abolished Alcα's KLC-binding activity and attenuated its peripheral transport, suggesting that Alcα's cleavage occurred, at least partly, en route to the cell surface. We further demonstrated that uncleavable mutant Alcα proteins readily accumulated on the cell surface and induced aberrant peripheral recruitment of KLC1 and kinesin heavy chain. Our observations suggest that Alcα is efficiently processed in part to minimize the inappropriate peripheral retention of kinesin-1. This role might exemplify the functional relevance of the constitutive cleavage of single-pass transmembrane proteins.     

Relationship between chloroplastic H2O2 and the salicylic acid response

Reactive oxygen species (ROS) act as signaling molecules for regulating plant responses to abiotic and biotic stress and there exist source- and kind-specific pathways for ROS signaling. Recently, we created a novel system for producing H₂O₂ in Arabidopsis chloroplasts by chemical-dependent thylakoid membrane-bound ascorbate peroxidase (tAPX) silencing using an estrogen-inducible RNAi method. Microarray analysis revealed that the expression of a large set of genes was altered in response to tAPX silencing, some of which are known to be involved in pathogen response/resistance. Furthermore, we found that tAPX silencing enhances the levels of salicylic acid (SA) and the response to SA, a central regulator for biotic stress response. In this addendum, we describe the relationship between chloroplastic H₂O₂ and SA in stress response, and discuss the function of the kind- and source-specific ROS signaling in SA-mediated stress response.