1.17.5 Adhesion Molecule Definition

Adhesion Molecule Definition is a description of a protein positioned at the surface of a cell that mediates physical attachment to a corresponding binding partner, whether an adhesion molecule on the surface of an adjacent cell or a component of the surrounding extracellular matrix, thereby serving as the fundamental molecular unit through which the broader process of cell adhesion is physically carried out.

Conceptual Basis

The Molecular Unit Underlying Physical Attachment

An adhesion molecule constitutes the specific molecular entity responsible for forming a physical binding interaction at the cell surface, such that the presence, abundance, and binding activity of particular adhesion molecules directly determines whether, and how strongly, a given cell attaches to a specific binding partner.

Defined by Its Binding Partner and Location

An adhesion molecule is characterized both by its location at the cell surface, positioning it to engage in extracellular binding interactions, and by the specific identity of the partner molecule it is capable of binding, whether that partner is another adhesion molecule on a neighboring cell or a structural component of the extracellular matrix.

Categories of Adhesion Molecule

Molecules Mediating Cell-Cell Binding

One category of adhesion molecule mediates cell-cell adhesion, binding directly to a corresponding adhesion molecule presented on the surface of an adjacent cell, and thereby physically linking the two cell surfaces together at the site of binding.

Molecules Mediating Cell-Matrix Binding

Another category of adhesion molecule mediates cell-matrix adhesion, binding directly to specific structural components of the surrounding extracellular matrix, and thereby physically anchoring the cell to its local structural environment rather than to another cell.

Structural Features

Extracellular Binding Region

An adhesion molecule characteristically possesses a portion extending outward from the cell surface into the extracellular space, structured to specifically recognize and bind its corresponding partner molecule, whether that partner is located on a neighboring cell or within the extracellular matrix.

Intracellular Region Linked to the Cytoskeleton

Many adhesion molecules also possess a portion extending into the interior of the cell, frequently linked through adaptor proteins to the internal cytoskeletal framework, coupling the extracellular binding event to the cell's internal structural network and enabling mechanical forces at the adhesive contact to be transmitted throughout the cell.

Functional Significance

Determining Adhesive Specificity and Strength

Because different adhesion molecules bind different specific partners with differing degrees of affinity, the particular set of adhesion molecules expressed by a given cell, and the abundance of each, are principal determinants of which specific adhesive interactions that cell is capable of forming, and how strong those interactions will be.

Coupling Physical Attachment to Intracellular Signaling

Beyond their purely structural binding function, many adhesion molecules also participate directly in intracellular signaling, such that the binding event itself, in addition to providing physical attachment, initiates signals influencing broader aspects of cellular behavior including proliferation and survival.

Relationship to Cell Adhesion and Cancer Cell Biology

The Basic Functional Unit of Cell Adhesion

An adhesion molecule constitutes the basic functional unit through which the broader process of cell adhesion, whether cell-cell or cell-matrix in nature, is physically carried out, positioning the study of individual adhesion molecules as foundational to understanding the broader adhesive behavior of a cell.

Relevance to Altered Cancer Cell Adhesion

Because the specific pattern of adhesion molecule expression and function directly determines a cell's adhesive relationships with its surroundings, changes in the abundance, distribution, or binding activity of particular adhesion molecules are closely associated with the altered adhesive behavior characteristic of cancer cells, linking the study of individual adhesion molecules directly to the broader analysis of cancer cell adhesion.