What is the difference between mushroom beta-glucan and other sourced beta-glucan?

Beta-glucans are groups of dietary fibres or polysaccharides composed of D-glucose monomers, linked by 1,3; 1,4 or 1,6-β-glucosidic bonds, and are naturally found in the cell wall of bacteria, fungi, mushrooms, and higher crops, such as cereals. 

Beta-glucans from different sources differ in structure. For example, cereal glucans are usually linear (1,3; 1,4)-β-glucans, yeast glucans are branched (1,3; 1,6)-β-glucans, mushroom glucans are linear (1,3)-β-glucans with (1,6)-linked-β-glucosyl or β-oligoglucosyl side chain. Mushroom beta-glucans have a more complex structure, have a much higher molecular weight and a part of mushroom beta-glucan is linked to proteins/peptides. The structural complexity of beta-glucans varies and is considered a primary determinant of activity. This is also the main accepted theory of why some mushrooms are more active than others and why mushroom beta-glucans are more immunologically active than other beta-glucans.

As Martin Powell, author of Medicinal Mushrooms, A Clinical Guide points out, “In contrast to the relatively inexpensive commercially available beta-glucans from yeast, mushroom beta-glucans have more diverse structures and, as a consequence, higher levels of immunological activity.”