Maltohexaose (Amylohexaose)

Maltohexaose-indocyanine green (MH-ICG) for near infrared imaging of endocarditis

Infectious endocarditis is a life-threatening disease, and diagnostics are urgently needed to accurately diagnose this disease especially in the case of prosthetic valve endocarditis. We show here that maltohexaose conjugated to indocyanine green (MH-ICG) can detect Staphylococcus aureus (S. aureus) infection in a rat model of infective endocarditis. The affinity of MH-ICG to S. aureus was determined and had a Km and Vmax of 5.4 μM and 3.0 X 10-6 μmol/minutes/108 CFU, respectively. MH-ICG had no detectable toxicity to mammalian cells at concentrations as high as 100 μM. The in vivo efficiency of MH-ICG in rats was evaluated using a right heart endocarditis model, and the accumulation of MH-ICG in the bacterial vegetations was 2.5 ± 0.2 times higher than that in the control left ventricular wall. The biological half-life of MH-ICG in healthy rats was 14.0 ± 1.3 minutes, and approximately 50% of injected MH-ICG was excreted into the feces after 24 hours. These data demonstrate that MH-ICG was internalized by bacteria with high specificity and that MH-ICG specifically accumulated in bacterial vegetations in a rat model of endocarditis. These results demonstrate the potential efficacy of this agent in the detection of infective endocarditis.

Targeted Bacteria-Specific 18F-Fluoro-Maltohexaose But Not FDG PET Distinguishes Infection From Inflammation

Comparative study on bread quality and starch digestibility of normal and waxy wheat (Triticum aestivum L.) modified by maltohexaose producing α-amylases

It is highly desirable to produce bread with both acceptable texture and health benefits. In this study, maltohexaose (G6) producing amylase AmyM and its truncation AmyM-TR2 from Corallococcus sp. strain EGB were used to determine their effects to bread quality and starch physicochemical properties. During bread fermentation, AmyM or AmyM-TR2 continuously degraded the starch, resulting in more obvious decrease in relative crystallinity, the ordered structure, pasting viscosities and gelatinization enthalpy of starch than in control. The dough treated with AmyM or AmyM-TR2 increased bread volume and slowly digestible starch content, decreased bread hardness, and extended bread shelf life and as compared with control, and the dough treated with AmyM-TR2 had better improvement effects than AmyM. The volume and slowly digestible starch content of bread from the treatment of AmyM-TR2 increased by 9.74% and 7.56% in normal wheat, 1.42% and 10.28% in waxy wheat as compared with AmyM, respectively. AmyM-TR2 affected the substrate targeting, proximity and structure disruption effects, which contributed to the degradation of more starch than AmyM.

AmyM, a Novel Maltohexaose-Forming α-Amylase from Corallococcus sp. strain EGB

A novel α-amylase, AmyM, was purified from the culture supernatant of Corallococcus sp. strain EGB. AmyM is a maltohexaose-forming exoamylase with an apparent molecular mass of 43 kDa. Based on the results of matrix-assisted laser desorption ionization-time of flight mass spectrometry and peptide mass fingerprinting of AmyM and by comparison to the genome sequence of Corallococcus coralloides DSM 2259, the AmyM gene was identified and cloned into Escherichia coli. amyM encodes a secretory amylase with a predicted signal peptide of 23 amino acid residues, which showed no significant identity with known and functionally verified amylases. amyM was expressed in E. coli BL21(DE3) cells with a hexahistidine tag. The signal peptide efficiently induced the secretion of mature AmyM in E. coli. Recombinant AmyM (rAmyM) was purified by Ni-nitrilotriacetic acid (NTA) affinity chromatography, with a specific activity of up to 14,000 U/mg. rAmyM was optimally active at 50°C in Tris-HCl buffer (50 mM; pH 7.0) and stable at temperatures of <50°C. rAmyM was stable over a wide range of pH values (from pH 5.0 to 10.0) and highly tolerant to high concentrations of salts, detergents, and various organic solvents. Its activity toward starch was independent of calcium ions. The Km and Vmax of recombinant AmyM for soluble starch were 6.61 mg ml(-1) and 44,301.5 μmol min(-1) mg(-1), respectively. End product analysis showed that maltohexaose accounted for 59.4% of the maltooligosaccharides produced. These characteristics indicate that AmyM has great potential in industrial applications.

PET imaging of bacterial infections with fluorine-18-labeled maltohexaose

A positron emission tomography (PET) tracer composed of (18)F-labeled maltohexaose (MH(18)F) can image bacteria in vivo with a sensitivity and specificity that are orders of magnitude higher than those of fluorodeoxyglucose ((18)FDG). MH(18)F can detect early-stage infections composed of as few as 10(5) E. coli colony-forming units (CFUs), and can identify drug resistance in bacteria in vivo. MH(18)F has the potential to improve the diagnosis of bacterial infections given its unique combination of high specificity and sensitivity for bacteria.