Contribution of cationic amino acids toward the inhibition of Arg-specific cysteine proteinase (Arg-gingipain) by the antimicrobial dodecapeptide, CL(14-25), from rice protein.

CL(14-25), a dodecapeptide, exhibits antimicrobial activity against Porphyromonas gingivalis with the 50% growth-inhibitory concentration (IC50 ) value of 145 µM, and arginine-specific gingipain (Rgp)-inhibitory activity. Kinetic analysis revealed that CL(14-25) is a mixed-type inhibitor, with inhibition constants (Ki and Ki ' values) of 1.4 × 10(-6) M and 4.3 × 10(-6) M, respectively. To elucidate the contributions of four cationic amino acid residues at the N- and C-termini of CL(14-25) toward Rgp-inhibitory activity, we investigated the Rgp-inhibitory activities of truncated and alanine-substituted analogs of CL(14-25). Rgp-inhibitory activities significantly decreased by truncated analogs, CL(15-25) and CL(16-25), whereas those of CL(14-24) and CL(14-23) were almost as high as that of CL(14-25). Rgp-inhibitory activities of alanine-substituted analogs, CL(R14A) and CL(R14A, R15A) also significantly decreased, whereas those of CL(K25A) and CL(R24A, K25A) were higher than that of CL(14-25). These results suggest that the arginine residue at position 15 substantially contributes to the Rgp-inhibitory activity and that the arginine residue at position 14 plays important roles in exerting Rgp-inhibitory activity. In this study, we demonstrated that CL(K25A) was a potent, dual function, peptide inhibitor candidate, exhibiting Rgp-inhibitory activity with Ki and Ki ' of 9.6 × 10(-7) M and 1.9 × 10(-6) M, respectively, and antimicrobial activity against P. gingivalis with an IC50 value of 51 µM.

Identification of myo-inositol hexakisphosphate (IP6) as a ß-secretase 1 (BACE1) inhibitory molecule in rice grain extract and digest.

Alzheimer's disease (AD) is widely considered to be caused by amyloid-ß peptide (Aß) accumulation in the brain. Aß is excised from amyloid-ß precursor protein through sequential cleavage by ß-secretase 1 (BACE1) and γ-secretase. Thus, BACE1 inhibition could prevent Aß accumulation. Here, we identified myo-inositol hexakisphosphate (IP6) as a BACE1 inhibitory molecule in rice grain extract and digest. The rice digest and IP6 significantly inhibited Aß production in neuroblastoma cells without cytotoxicity. These results suggested that rice components, including IP6, may be promising starting materials for the development of potent and safe drugs and/or food to prevent AD.

Dynactin is essential for growth cone advance.

Dynactin is a multi-subunit complex that serves as a critical cofactor of the microtubule motor cytoplasmic dynein. We previously identified dynactin in the nerve growth cone. However, the function of dynactin in the growth cone is still unclear. Here we show that dynactin in the growth cone is required for constant forward movement of the growth cone. Chromophore-assisted laser inactivation (CALI) of dynamitin, a dynactin subunit, within the growth cone markedly decreases the rate of growth cone advance. CALI of dynamitin in vitro dissociates another dynactin subunit, p150(Glued), from dynamitin. These results indicate that dynactin, especially the interaction between dynamitin and p150(Glued), plays an essential role in growth cone advance.