Carbohydrate Binding Module Family 1

This page is currently under construction. This means that the Responsible Curator has deemed that the page's content is not quite up to CAZypedia's standards for full public consumption. All information should be considered to be under revision and may be subject to major changes.

• Author: ^^^Markus Linder^^^
• Responsible Curator: ^^^Markus Linder^^^

---

CAZy DB link

https://www.cazy.org/CBM1.html

Ligand specificities

The family 1 CBMs are found mainly in fungal enzymes [1, 2]. Early work showed that family 1 CBMs bind to cellulose [3] and that some, but not all, family 1 CBMs bind to chitin as well [4]. There is also a contribution of CBMs in binding to lignin, but this binding was shown to be non-specific as it was easily blocked by surfactants [5]. Based on NMR measurements it was shown that family 1 CBMs could bind to cellohexaose, but not to shorter cellotriose and cellobiose [6].

Figure 1. Top. A backbone trace of the T.reesei Cel7A CBM showing residues that have been identified as important for the interaction with cellulose. Below. the structure turned 90 degrees to show how the aromatic residues align with pyronose rings in a cellulose molecule.

Structural Features

Structurally the family 1 CBMs are distinct from other families. They are relatively small, only about 35 amino acids and have two or three disulphide bridges that stabilize their fold [7]. This type of fold is called a cystine knot and is also found in a family of toxins, called conotoxins produced by cone shells [8]. This structure is rigid and on the CBM there are three aromatic residues (tyrosines or tryptophans) that align so that their spacing is the same as every second pyranose ring on cellulose. Together with some hydrogen bond forming side chains this triad of aromatic residues form a binding face that docks onto the cellulose surface. It has also been shown using synthesised peptides that carbohydrates added to the CMBs affect their binding properties [9]

Functionalities

The CBMs affect enzyme activity by bringing the enzymes close to the cellulose surface [10], but there are reports that family 1 CBMs can disrupt the crystalline structure of cellulose as well [11]. Family 1 CBMs are found widely in fungal cellulases, also in several enzymes that are not active on cellulose such as mannanase [12] and acetyl xylan esterase [13]. Also swollenins have been found to contain family 1 CBMs [14].

Family 1 CBMs have been used in different types of applications such stabilizing colloid dispersions of drugs by mediating binding to nanocellulose [15].

Family Firsts

Family 1 CBMs were found first in studies on the Trichoderma reesei Cel7A enzyme (then called cellobiohydrolase I, CBHI) using papain for fragmentation. These studies revealed that Cel7A had a “bifunctional” organization with one part binding strongly to cellulose and the other part containing the catalytic machinery [16]. It was noted that sequences homologous to the smaller cellulose binding part was found in many fungal cellulases and that a synthetic analogue functioned identically to the native fragments produces by proteolysis [3]. The synthetic version of the cellulose binding domain was then analysed by NMR and its structure was determined [7]. With the structure determined the research then led to a number of structure-function studies identifying the amino acids responsible for binding [17] and changing of binding properties by protein engineering [18].

References

Error fetching PMID 24767427:
Error fetching PMID 26390127:
Error fetching PMID 8702902:
Error fetching PMID 14687972:
Error fetching PMID 9175871:
Error fetching PMID 2554967:
Error fetching PMID 19858200:
Error fetching PMID 21111611:
Error fetching PMID 12199698:
Error fetching PMID 9792173:
Error fetching PMID 7549870:
Error fetching PMID 26307003:

3. Johansson, G., Ståhlberg, J., Lindeberg, G., Engström, Å., Pettersson, G. Isolated Fungal Cellulose Terminal Domains and a Synthetic Minimum Analogue Bind to Cellulose. FEBS Lett. 1989; 243, 389–393.

15. Varjonen, S.; Laaksonen, P.; Paananen, A.; Valo, H.; Hähl, H.; Laaksonen, T.; Linder, M. Ben. Self-Assembly of Cellulose Nanofibrils by Genetically Engineered Fusion Proteins. Soft Matter 2011, 7, 2402–2411.

16. van Tilbeurgh, H.; Tomme, P.; Claeyssens, M.; Bhikhabhai, R.; Pettersson, G. Limited Proteolysis of the cellobiohydrolase I from Trichoderma Reesei Separation of Functional Domains. FEBS Lett. 1986; 204, 223–227.

18. Linder, M.; Nevanen, T.; Teeri, T. T. Design of a pH-Dependent Cellulose-Binding Domain. FEBS Lett. 1999;447,13–16.