Naoshi Dohmae

Klotho Protein Deficiency Leads to Overactivation of μ-Calpain

The klotho mouse is an animal model that prematurely shows phenotypes resembling human aging. Here we report that in homozygotes for the klotho mutation (kl −/−), αII-spectrin is highly cleaved, even before the occurrence of aging symptoms such as calcification and arteriosclerosis. Because αII-spectrin is susceptible to proteolysis by calpain, we examined the activation of calpain in kl −/− mice. m-Calpain was not activated, but μ-calpain was activated at an abnormally high level, and an endogenous inhibitor of calpain, calpastatin, was significantly decreased. Proteolysis of αII-spectrin increased with decreasing level of Klotho protein. Similar phenomena were observed in normal aged mice. Our results indicate that the abnormal activation of calpain due to the decrease of Klotho protein leads to degradation of cytoskeletal elements such as αII-spectrin. Such deterioration may trigger renal abnormalities inkl −/− mice and aged mice, but Klotho protein may suppress these processes.

Functional Analysis of PsbZ in Photosystem II from the Thermophilic Cyanobacterium Thermosynechococcus elongatus BP-1

PsbZ is a membrane protein of 6.5 kDa found in photosystem II (PSII) complexes from cyanobacteria to land plants. The two helices of PsbZ are located on the perimeter of the dimer near CP43 and PsbK in the cyanobacterial PSII structure. In tobacco and Chlamydomonas reinhardtii, psbZ knockout leads to reduce amounts of the minor antenna protein CP26. However, CP26 is not found in the cyanobacterial thylakoids. The function of PsbZ in cyanobacteria is still not clear. In this work, we deleted psbZ gene in the thermophilic cyanobacterium, Thermosynechococcus elongatus BP-1 to analyze the function of PsbZ. No difference was observed in the growth under various light conditions, and in the oxygen-evolving activities between the wild type and the mutant. However, the oxygen-evolving activity in the mutant PSII complexes purified by Ni-affinity chromatography was lower than those in the purified wild-type PSII complexes. Electrophoretic profile of the mutant PSII complexes revealed that most of PsbK band had disappeared but no significant release of the extrinsic proteins was observed. N-terminal amino acid sequences of PsbK and PsbM/Ycf12 bands showed that most of Ycf12 as well as PsbK was lost in the mutant PSII complexes. These indicate that PsbZ is required for the stable binding of PsbK and Ycf12 to the PSII core. We suggest that Ycf12 is the unidentified X1 polypeptide (Loll et al. 2005) that is observed near PsbZ and PsbK in the crystal structure of the PSII complex.