1-Methyl-L-Histidine

The growing demand of pharmaceutical-grade plasmid DNA (pDNA) suitable for biotherapeutic applications fostered the development of new purification strategies. The surface plasmon resonance technique was employed for a fast binding screening of l-histidine and its derivatives, 1-benzyl-L-histidine and 1-methyl-L-histidine, as potential ligands for the biorecognition of three plasmids with different sizes (6.05, 8.70, and 14 kbp). The binding analysis was performed with different isoforms of each plasmid (supercoiled, open circular, and linear) separately. The results revealed that the overall affinity of plasmids to l-histidine and its derivatives was high (KD > 10(-8) M), and the highest affinity was found for human papillomavirus 16 E6/E7 (K(D) = 1.1 × 10(-10) M and KD = 3.34 × 10(-10) M for open circular and linear plasmid isoforms, respectively). L-Histidine and 1-benzyl-L-histidine were immobilized on monolithic matrices. Chromatographic studies of L-histidine and 1-benzyl-L-histidine monoliths were also performed with the aforementioned samples. In general, the supercoiled isoform had strong interactions with both supports. The separation of plasmid isoforms was achieved by decreasing the ammonium sulfate concentration in the eluent, in both supports, but a lower salt concentration was required in the 1-benzyl-L-histidine monolith because of stronger interactions promoted with pDNA. The efficiency of plasmid isoforms separation remained unchanged with flow rate variations. The binding capacity for pDNA achieved with the l-histidine monolith was 29-fold higher than that obtained with conventional L-histidine agarose. Overall, the combination of either L-histidine or its derivatives with monolithic supports can be a promising strategy to purify the supercoiled isoform from different plasmids with suitable purity degree for pharmaceutical applications.

We describe the significant difference in the O2 binding affinities of human serum albumin (HSA) incorporating 5,10,15,20-tetrakis{alpha,alpha,alpha,alpha- o-(1'-methylcyclohexanamido)phenyl}porphinatoiron(II) with a covalently linked 1-methyl-L-histidine or 3-methyl-L-histidine [HSA-FeP(1-MHis), HSA-FeP(3-MHis)]. The HSA-FeP(3-MHis) showed an extraordinarily high O2 binding affinity ( P1/2 = 0.2 Torr, 25 degrees C, pH 7.4), which is close to those of relaxed-state hemoglobin and myoglobin. However, replacement of the 3-methyl-L-histidine moiety in FeP(3-MHis) by 1-methyl-L-histidine caused a 35-fold reduction in O2 affinity; the P 1/2 value of HSA-FeP(1-MHis) (22 Torr, 37 degrees C, pH 7.4) is almost identical to that of human red blood cells. Results of kinetic studies indicate that the low O2 binding affinity of FeP(1-MHis) is predominantly manifested in the high O2 dissociation rate constant. In a toluene solution, an identical relationship in the O2 binding property was similarly observed for FeP(1-MHis) and FeP(3-MHis). The axial Fe-N(1-MHis) coordination might be restrained by steric interaction between the 4-methylene group of the histidine and the porphyrin plane.

Myosin, a major muscle protein, can be solubilised in a low ionic strength solution containing L-histidine (His). To elucidate which chemical constituents in His are responsible for this solubilisation, we investigated the effects of 5mM His, imidazole (Imi), L-α-alanine (Ala), 1-methyl-L-histidine (M-his) and L-carnosine (Car) on particle properties of myosin suspensions and conformational characteristics of soluble myosin at low ionic strength (1 mM KCl, pH 7.5). His, Imi and Car, each containing an imidazole ring, were able to induce a myosin suspension, which had small particle size species and high absolute zeta potential, thus increasing the solubility of myosin. His, Imi and Car affected the tertiary structure and decreased the α-helix content of soluble myosin. Therefore, the imidazole ring of His appeared to be the significant chemical constituent in solubilising myosin at low ionic strength solution, presumably by affecting its secondary structure.