Analysis of G-Block Distributions and Their Impact on Gel Properties of in Vitro Epimerized Mannuronan

Abstract

2 This paper reports a study of the distribution and function of homopolymeric guluronic acid blocks (G-blocks) in enzymatically modified alginate. High molecular weight mannuronan was incubated with one native (AlgE6) and two engineered G-block generating mannuronan C-5 epimerases (AlgE64, and EM1). These samples were found to contain G-blocks with a DP ranging from 20 to approximately 50, lacking the extremely long G-blocks (DP>100)found in algal alginates Calcium gels from epimerised materials were highly compressible and exhibited higher syneresis and rupture strength, but lower Youngs modulus than gels made from algal polymers of similar G-content. Addition of extremely long G-blocks to the epimerized alginate resulted in decreased syneresis and rupture strength, and an increased Young's modulus that can be explained by reinforcement of the crosslinking zones at the cost of length and/or numbers of elastic segments. The presence and impact of these extremely long G-blocks found in natural alginates suggest that alginate gels can be viewed as a nanocomposite material.

Direct Determination of Chitosan–Mucin Interactions Using a Single-Molecule Strategy: Comparison to Alginate–Mucin Interactions

“…The molecular weights of the chitosans were estimated from the determined [η] using the Mark-Houwink-Kuhn equation with the reported parameters [59]. The molecular weights of the alginates were determined as reported [60]. The parameters of the chitosan and alginate samples are summarized in Table 1.…”

Biosynthesis and Function of Long Guluronic Acid-Blocks in Alginate Produced by Azotobacter vinelandii

“…In a previous paper we reported that gels made from in vitro epimerized poly-M lacks the fraction of very long G-blocks that are ever-present in brown seaweed alginates and thereby display an unusually low Young's modulus and a high degree of syneresis. 22 In this study, we compare the G-block distributions and gel properties of A. vinelandii alginate with in vitro epimerized poly-M and brown seaweed alginate. Data on the epimerization pattern obtained by epimerization with full length AlgE1, as well as its individually active G-block forming A-modules is also presented.…”

“…VLG is an important factor since alginate gels made from poly-M in vitro epimerized with AlgE6 in the range of 29−68% G all has a syneresis between 60 and 70%, despite a low amount of alternating sequences,22 while gels made from deacetylated A. vinelandii alginate has a syneresis below 40%.Altogether, the differences in G-block distribution (Figure 3) and syneresis (Figure 4B) between AlgE6 epimerized poly-M and A. vinelandii alginates shows that the latter contains a fraction of VLG. This results in a different organization of the hydrogel network than the short to intermediate length Gblocks found in AlgE6 epimerized poly-M. As expected the presence of O-acetyl groups impairs gel formation, giving weaker gels.…”

Structural and Functional Characterization of the R-modules in Alginate C-5 Epimerases AlgE4 and AlgE6 from Azotobacter vinelandii

“…Although the intrinsic inflexibility of the alginate chain increases in the order MG Ͻ MM Ͻ GG (4), the selectivity for binding of cations and gel-forming properties is mainly linked to the G-blocks (3,5,6). Recently, it has been shown that G-blocks larger than 100 consecutive residues are essential for forming stable calcium gels (7).…”