Question

74.Adhesive proteins of connective tissue: examples, structure and functions.

(please more explanatıon Im medicine student) thank you...

Answer 1

Introduction

adhesive proteins of connective tissue:

Connective tissue has made up of three main components as below

1. Ground substance

2. Fibers

3. Cells    Ground substance has a clear, colorless, viscous fluid that fills the space between the cells and fibers. It is made up of proteo-glycans and cell adhesion proteins that allow the connective tissue to act as the glue for the cells to attach to the matrix like the ligation. The ground substance functions as a molecular sieve for substances to travel between blood capillaries and cells.

the function of connective tissue  

1. Binding and supporting.
2. Protecting.
3. Insulating.
4. Storing reserve fuel.
5. Transporting substances within the body.

adhesive protein :

Cell adhesive proteins are mediate important bidirectional interactions between cells and the extracellular matrix like a connecting link between both. They provide an interactive interface between the extracellular chemical and physical environment and the cellular scaffolding and signaling machinery of the cell in the body. This dynamic , intensive regulation of intracellular processes and the matrix is mediated by membrane receptors such as the integrins, as well as many other components that comprise the adhesive protein. Adhesive protein constituents assemble themselves into various types for cell adhesion structures that give them molecular complexity and they can change over time. These cell adhesions play crucial roles in cell migration, proliferation, and determination of cell fate.

Cell-matrix interactions are mediated by the adhesion receptors and which have to the formation of multi-protein adhesion structures that can interact with the actin filament which are in the cytoskeleton at the cell interior; collectively, they are called cell-matrix adhesion complexes. These complex adhesive proteins act as vital information processing centers that enable cells to sense numerous extracellular signals that convey information about the chemistry, geometry, and physical properties of the extracellular matrix.

adhesive protein is also called Cell-matrix adhesion. it is the interaction of a cell with the extracellular matrix, mediated by multi-protein adhesion structures like focal adhesions, fibrillar adhesions, and podosomes.

The extracellular matrix is a network of extracellular molecules that are secreted locally to ensure cell and tissue cohesion. The extracellular matrix also serves as a reservoir for extracellular signaling molecules that control cell growth, migration, and differentiation. The major classes of connective tissue adhesion molecules are proteoglycans, collagens, and multi-adhesive matrix proteins (e.g. laminin, fibronectin). For the stability in tissues, cells are linked to the extracellular matrix through cell adhesion receptors (e.g. integrins). A specialized form of the extracellular matrix that underlies the basal side of polarized epithelial cell sheets to separate them from the underlying connective tissue is the basal lamina.

example and structure

Laminin - Laminin is a major structural multidomain adhesive protein of at the basement membranes, has been shown to many of a variety of biological activities. Prominent among those is a mediation of cell attachment as well as influences on cellular proliferation, differentiation, and motility. Distinct domains of laminin have been identified which carry these activities in the extracellular matrix. The active sites on laminin are recognized by cellular receptors, many of which belong to the integrin class of heterodimeric transmembrane proteins. These are in direct contact with intracellular proteins and mediate signals from the extracellular matrix to the cytoskeleton and possibly to another intracellular regulatory system.

structure- it has Globular and rodlike domains are arranged in an extended four-armed, cruciform shape that is well suited for mediating between distant sites on cells and other components of the extracellular matrix. The a-helical coiled-coil domain of the long arm is involved in the specific assembly of the three chains of laminin and is the only domain composed of multiple chains. It is terminated by a large globular domain composed of five homologous subdomains formed by the COOH-terminal part of the A chain. Sites for receptor-mediated cell attachment and promotion of neurite outgrowth reside in the terminal region of the long arm.

Fibronectin -Fibronectin is also involved in many cellular processes, including tissue repair, embryogenesis, blood clotting, and cell migration and adhesion. Fibronectin exists in two main forms: 1) as an insoluble glycoprotein dimer that serves as a linker in the extracellular matrix, and; 2) as a soluble disulfide-linked dimer found in the plasma (plasma FN). The plasma form is synthesized by hepatocytes, and the ECM form is made by fibroblasts, chondrocytes, endothelial cells, macrophages, as well as certain epithelial cells. Fibronectin mainly serves as a general cell adhesion protein molecule by anchoring cells to collagen or proteoglycan substrates. it is also can serve to organize cellular interaction with the extracellular matrix by binding to different components of the extracellular matrix and to membrane-bound fibronectin receptors on cell surfaces

structure- it showing the repeated arrangement of the three module types, as well as key binding sites. Twelve types I modules make up the amino-terminal and carboxy-terminal region of the molecule and are involved mainly in fibrin and collagen binding. Only two type II modules are found in fibronectin. They are instrumental in binding collagen. The most abundant module in fibronectin is Type III, which contains the RGD fibronectin receptor recognition sequence along with binding sites for other integrins and heparin.