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Figure 1. Carbohydrate array assays of WfCBM101. The binding of WfCBM101 to agarose and other galactans in red algae (A), and several other polysaccharides (B) was evaluated. κ-Car, κ-carrageenan. ι-Car, ι-carrageenan. Alg, alginate. An-FUC, sulfated fucan from Ascophyllum nodosum. CSA, chondroitin sulfate A sodium salt. HA, hyaluronic acid. Pec, pectin. Three repeats were conducted for each polysaccharide.
The first characterized member in the CBM101 family is WfCBM101 [1]. The CBM WfCBM101 bound to agarose and displayed a weak affinity to porphyran (Fig. 1). It was incapable of binding to the other polysaccharides that were examined, including κ-carrageenan, ι-carrageenan, alginate, sulfated fucan, chondroitin sulfate A sodium salt, hyaluronic acid, and pectin. Furthermore, WfCBM101 bound to agarose tetrasaccharide, but not to porphyran tetrasaccharide. It was reported porphyran consists of approximately 30% structural units of agarose [2]. It is thus speculated that the weak affinity of WfCBM101 for porphyran is attributed to the structural heterogeneity of porphyran.
Structural Features
An AlphaFold2 model predicts that WfCBM101 has a β-sandwich fold.
Functionalities
To evaluate the feasibility of WfCBM101 as a tool in the in situ investigation of porphyran, a fluorescent probe was constructed by fusing WfCBM101 with a green fluorescent protein. The in situ visualization of agarose in the red alga Gelidium amansii was realized by utilizing the fluorescent probe [1].
Taking WfCBM101 as the query sequence, 15 modules were retrieved from the NCBI database by the BLASTP program (E-value < e-5). There are eight modules adjacent to catalytic domains which are divided into the GH16_16 subfamily or GH86 family. According to the CAZy database, the [[GH16]_16 subfamily and GH86 family have members that degrade agarose. This implies that these eight modules might bind to agarose; however, this requires further investigation.
Family Firsts
First Identified
The first member WfCBM101 is a component of a GH86 β-agarase (unpublished data) from a marine bacterium Wenyingzhuangia fucanilytica CZ1127T [3].
First Structural Characterization
No experimentally determined three-dimensional structure has been solved in this CBM family.
