Structural Characterization of Glucans by Proton NMR

(1-3,1-6)-ß-Glucans are composed of glucosyl repeat units (GRUs) with a main chain and side chains.  The main chain is composed of (1-3)-ß-linked GRUs while the side chains are composed of (1-6)-ß-linked GRUs connected to the main chain at the 6-position of a branch point GRU in the main chain.  Molecular weight, side chain branching frequency and side chain length are important properties for defining structure/property relationships.  

We have examined many glucan isolates including the following:

• Linear yeast (1-3,1-6)-ß-glucan from Candida glabrata (1)
• Cyclic hyphae (1-3,1-6)-ß-glucan from Candida albicans (2)
• Linear (1-3,1-6)-ß-glucan from Candida auris (3)
• (1-6)-ß-glucan from Malassezi sympodialis (4)
• Marine yeast (1-3,1-6)-ß-glucan from Penaeus monodon (5)

The 800 MHz  proton NMR spectra below provide a comparison of linear (bottom) and cyclic (top) (1-3,1-6)-ß-glucans (1,2).  Note that the cyclic glucan does not exhibit a proton resonance for the non-reducing terminus observed for the main backbone chain.  Proton resonance for the reducing terminus of the linear glucan is difficult to observed due to overlap with the anomeric proton resonance of the side chain non-reducing terminus.  The linear glucan was isolated from Candida glabrata (1) while the cyclic glucan was isolated from C. albicans hyphae (2).  Legend:  H1: anomeric protons of the main backbone chain (BC) glucosyl repeat units (GRUs); RT: main backbone chain reducing terminus anomeric proton; SRT: anomeric proton of the GRU second to RT; NRT: main backbone chain non-reducing terminus anomeric proton; H1SC: anomeric protons of the side chain (SC) GRUs; H6SC: one of the methylene protons in the (1-6)-linkage of the side chain GRUs; SCNRT: side chain non-reducing terminus; SC1: first GRU in the side chain attached to the branch point (Br).

Selected References:

(1)  “New Insights into the Structure of (1-3,1-6)-D-ß-Glucan Side Chains in the Candida glabrata Cell Wall,” Douglas W. Lowman, Lara J. West, Daniel W. Bearden, Michael F. Wempe, Trevor D. Power, Harry E. Ensley, Ken Haynes, David L. Williams, Michael D. Kruppa, PloS ONE, 6(11): e27614 (2011)

(2) "Structural features in Candida albicans hyphal glucan provide a basis for differential innate immune recognition of hyphae versus yeast,"  Lowman, D. W., Greene, R. R., Bearden, D. W., Kruppa, M., Pottier, M., Monteiro, M., Soldatov, D., Ensley, H. E., Cheng, S.-C., Netea, M. G., Williams, D. L.  Novel  J. Biol Chem 289 (6) 3432-43, 2014.

(3) "Transcriptional and functional insights into the host immune response against the emerging fungal pathogen Candida auris.," Mariolina Bruno, Simone Kersten, Judith M. Bain, Martin Jaeger, Diletta Rosati, Michael D. Kruppa, Douglas W. Lowman, Peter J. Rice, Bridget Graves, Zuchao Ma, Y. Ning Jiao, Anuradha Chowdhary, George Renieris, Frank L. van de Veerdonk, Bart-Jan Kullberg, Evangelos, J. Giamarellos-Bourboulis, Alexander Hoischen, Neil A. R. Gow, Alistair J. P. Brown, Jacques F. Meis, David L. Williams, Mihai G. Netea, Nature Microbiology, August 24 (2020) 1-16, https://doi.org/10.1038/s41564-020-0780-3

(4) “Identification of (1-6)-ß-D-glucan as the major carbohydrate component of the Malasezzia sympodialis cell wall,” Michael D. Kruppa, Douglas W. Lowman, Yu-Han Chen, Christine Selander, Annika Scheynius, Mario Monteiro and David L. Williams, Carbohydrate Research, 344, 2474-2479 (2009)

(5) "Immune gene expression profile of Penaeus monodon in response to marine yeast glucan application and white spot syndrome virus challenge," Wilson, W., Lowman, D., Antony, S.P., Puthumana, J., Singh, I.S.B., Philip, R. Fish & Shellfish Immunology 43:346-356, 2015