GAG (---)→attaract cations (+)→
more concentrate → osmotic pressure
↑↑↑→ water income → keep in ECM
The extracellular matix (ECM)
Three types of molecules are abundant in the extracellular matrix of all tissues:
1. proteoglycan: a glycoproteins, high viscosity, it can bound variety of ECMs
2. Collagen fibers: provide mechanical strength and resilience.
3. Soluble multiadhesive matrix proteins: bind to and cross-link cell-
surface adhesion receptors and other ECM components
Fibronectins connect many cells to fibrous collagens and other matrix components
Fibronectin = example of “adhesive” ECM protein
Is a protein with multiple domains with number of specific binding sites for macromolecules and for receptors on cell surface.
Plasma Fibronectin; soluble, circulates in the blood and other body fluids → enhances blood clotting, wound healing and phagocytosis
Fibronectin Fibrils; insoluble → assemble on surface of cells & deposited in ECM
Fibrils assemble on surface of cells via fibronectin-binding integrins.
Usually aligned with adjacent intracellular actin fibres.
Fibronectin is a dimer, two chains linked via disulfide bonding at the carboxyl terminus
Fibrin, heparan sulfate proteoglycan, and collagen:
– bind to distinct regions in fibronectin
– integrate fibronectin fibers into the extracellular matrix network
Some cells express integrin receptors that bind to the Arg-Gly-Asp (RGD) sequence of fibronectin.
At least 20 different forms of fibronectin have been identified.
– All of them arise from alternative splicing of a single fibronectin gene.
The soluble forms of fibronectin are found in tissue fluids.
The insoluble forms are organized into fibers in the extracellular matrix.
Fibronectin fibers consist of crosslinked polymers of fibronectin homodimers.
Fibronectin proteins contain six structural regions.
– Each has a series of repeating units.
RGD is the letter
designation for the amino acids Arginine, Glycine and Aspartic Acid
FIBRONECTINS: attach cells to collagen matrices Regulates cell shape/cytoskeleton
Dimers of two similar polypeptides linked by disulfide bonds Forms fibrils when exposed to cells expressing intergrins
Circulating fibronectin can bind to fibrin, with the result that platelets associate at the site of blood clots via integrin binding
Specific tripeptide sequence RGD is important role of the cell-bind region of fibronectin is require adhesion of cells
•Cell binding region
•Type III repeat/binds integrins
Integrins mediate linkage between fibronectin in the extracellular matrix and the cytoskeleton
Green: integrin Red: actin
Stress fiber are long bundles of actin microfilamenht that radiate inward from points where the cell contacts a substratum
Adhesive interactions in motile and nonmotile cell
Integrins relay signals between cells and their 3D environment Integrins interact with ECM: regulation of integrin-mediated
adhesion and signaling controls cell movement
Human fibroblast Cell grown directly on the flat surface of culture dish (a)
On 3D ECM components (b)
Integrins cluster into adhesive structures with various morphologies in nonepithelial cell
At least 12 distinct α- subunits and 9 β- subunits identified;
single subunit can associate with more than one partner
Difficult to crystallize and therefore 3D structures not readily available Cloning experiments
indicate that integrins have short cytoplasmic tail (~ 50 amino acids) and 4 Ca2+ binding sites identified in the a subunit
Numerous disulfide bonds- difficult identify all of them
Muscular dystrophy: connections between the ECM and cytoskeleton are defective
About 1/3300 boys, heat or lung failure
Mutation of dystrophin (a cytoslic protein), bind to dystroglycan
Dystroglycan: α-subunit (peripheral protein) plus β-subunit
(transmembrane protein); the a- subunit also has O-linked
oligosaccharides to bind various basal lamina components
DGC (dystrophin glycoprotein
complex) links extracellular matrix to the cytoskeleton and singling pathways enzyme for muscle’s function
Mutations in components of this pathway (e.g. muscular dystrophy) results in mechanical instability of muscle cells.
Duchenne muscular dystrophy (DMD) 裘馨氏肌肉萎縮症
(Dystrophin)，此症患者的細胞內完全缺少肌肉 萎縮蛋白，肌纖維膜變得無力脆弱，經年累月伸 展後終於撕裂，肌細胞易死亡。
Affects structure (DGC) involved in linking muscle cell to basal lamina This structure provides strength to cell membrane
disruption leads to weakening of mechanical stability of cell Affects cytosolic adapter protein-Dystrophin
Interacts with dystroglycan (glycoprotein
Model for integrin activation
X-ray crysal structure
Ligand bind and induced conformational change
Diversity of ligand-integrin interaction contributes to number biological processes
Cell-matrix adhesion is modulated by changes in the binding
activity and neumber of integrins
Integrin superfamily 的黏著分子主要參與細胞與細胞外基質的黏附，使細胞 得以附著而形成integration。此外，這些分子還參與白血球與血管內皮細 胞的黏附。
α鏈的分子量為120～180kD, β鏈的分子量為90～110kD,不同的α鏈或β鏈胺 基酸組成和序列有不同程度的同源性，在架構上有其共同的特點。
α subunits和β subunits組合構成並不是隨機的，多數α subunits只能與一 種β subunits結合成heterodimer，而大部分β subunits則可以結合數種不 同α subunits。目前依β subunits的不同將與動脈粥狀硬化相關的integrin superfamily分為3個不同的組。
Integrin在與ligand結合時所識別的只是ligand分子中由數個胺基酸組成的序 列，例如Arg-Gly-Asp ( RGD )序列。不同的integrin可以識別相同的序列或 同一個ligand中不同的序列。
Laminin and fibronectin provide an adhesive
substrate for cells
The Binding of Cytoskeleton to the Extracellular Matrix Through
the Integrin Molecule
Many cell-matrix and some cell-cell interactions are mediated
Immunoglobulin Superfamily CAMs (ICAMs)
Ca2+ independent cell-cell adhesion in neuronal and other tissue is mediated by CAMs (IgCAM) in the immunoglobulin
Movement of leukocytes into tissue depends on a precise sequence of combinatorially diverse set of adhesive interactions.
Movement across an endothelial cell layer of:
• Monocytes (macrophage precursors - cells that ingest foreign particles)
• Neutrophils (release antibacterial)
• T and B Lymphocytes (antigen-specific)
Movement is mediated by selectins, a class of CAMs specific for leukocyte/vascular cell interactions
• Activate integrin binds ICAM-1 and ICAM-2
• Cells move from the blood into infected or inflamed tissue
Immunoglobulin superfamily的家族成員眾多，且均與immunoglobulin 有一定的同 源性，其分子架構中含有多個90-100個胺基酸的Ig-like domains。廣泛分佈於 淋巴細胞、單核細胞、內皮細胞等多種細胞的表面。
重要的成員有intercellular adhesion molecule-1、2、3 ( ICAM-1、2、3）、
vascular cell adhesion molecule-1 ( VCAM-1 ) 和platelet-endothelial cell adhesion molecule ( PECAM )。
ICAM-1是最早發現的immunoglobulin superfamily 黏附分子之一，以後又相繼發現了ICAM-2和 ICAM-3，它們的胺基酸序列具有同源性，且都 可以結合LFA-1分子(一種integrin )。不同的
某些腫瘤細胞、上皮細胞、肝細胞、平滑肌細 胞等，IL-1、TNF- α 、和LPS可促進ICAM-1分 子的表現；ICAM-2則分佈較局限，主要表現在 血管內皮細胞；而ICAM-3表現在T細胞、單核 細胞 。
IgCAMs comprise a diverse group of adhesion receptors, that are defined by the presence of one or several Ig folds; classical
Neuronal CAM (NCAM) is implicated in neuronal guidance and establishment of new synapses
NCAM forms homotypic contacts
Intercellular CAM (ICAM) interacts heterotypically with integrins CAMs differ widely in their cytoplasmic binding partners
Selectins: mediate transient cell-cell adhesion in the bloodstream
White blood cells (WBCs) utilize the adhesive properties of selectins (and integrins) in order to move: blood ↔ tissue.
• Selectins are “lectins” – carbohydrate binding proteins. (Ca2+ dependent)
• TM protein with a highly conserved lectin
domain that binds to a specific oligosaccharide.
• Transient, calcium-dependent interactions.
• Selectin types:
9 L-selectin: WBCs
9 P-selectin: platelets and endothelial cells 9 E-selectin: activated endothelial cells
lectins” – carbohydrate binding proteins. (Ca2+
L、P和E分別表leukocyte , platelet和endothelium , 是最初發現相應selectin 分子的三種細胞，故得名。
P-selectin，分子量 140KD，由單核巨細胞跟內皮細胞形成，貯存於血小板的 α顆粒及內皮細胞的Weibel-Palade小體。當受到thrombin跟histamine刺激 時，P-selectin會迅速到達血小板或內皮細胞表面，介導白血球與內皮細胞 的起始黏附。
E-selesctin，分子量115KD，正常的內皮細胞表面並無E-selesctin存在，細 胞內也沒有儲存。當受到IL-1及TNF- α等細胞因子的刺激時，會活化內 皮細胞，刺激E-selesctin的合成。 E-selesctin會幫助白血球與內皮細胞的 黏附作用。
L-selesctin廣泛存在於各種白血球的表面，參與發炎部位白血球的出血管過 程。白血球表面L-selesctin分子上的sLeA與活化的內皮細胞表面的P- selesctin及E -selesctin之間的識別與結合，可召集血液中快速流動的白血 球在發炎部位的血管內皮上減速滾動（即透過黏附、分離、再黏
MACROMOLECULAR ORGANIZATION OF ECM
Movement of leukocytes into tissue depends on a precise sequence of combinatorially diverse set of adhesive intereaction
Bacterial, infection or inflammation → tissue dysfunction → blood
(leukocyte) → expressed special adhesion molecules at endothelial
surface → bind leukocyte → induced adhesion molecule activation →
extravasation → extracellular ……….
P-selectin, a lectin (protein that binds carbohydrates) on activated endothelial cells, binds a specific ligand (an oligosaccharide sequence) on T cells
PAF (Platelet Activating Factor - a phospholipid) activates integrin on the leukocyte surface
CAM directly bind to leukocyte
1. Endothelium activatioin → selectin or carbohydrate ligand →weak, reversible binding
2. Infection or inflammation signal → chemokines or PAF → expressed special molecules → attached leukocyte
3. Additional activation dependent CAM, integrins → strong adhesion
Multi - - step Model of Leukocyte step Model of Leukocyte
Adhesion and Extravasation
Adhesion and Extravasation
Leukocyte-adhesion deficiency 淋巴球黏力缺失症
Leukocyte did not extravasation
Unlike animals, plants do not replace or repair old or damaged cells or tissues; only grow new organs
Plant only four broad types of cells (form four basic classes of tissue) 1.dermal tissue: interact with environment
2.vasculat tissue: transport water and dissolved substances 3.ground tissue: space filling
4.sporogenous tissue: forms the reproductive organs
Contain polysaccharides: cellulose (tensile 張力 拉力strength), hemicelluose
Allow soluble factor to pass to cell membrane, but less permeable than animal cell matrix
Functions of cell walls:
Mechanical strength--> plant heights
Glue cells together--> dictate the way in which plant develop Exoskeleton--> control cell shapes
Control balance between cell turgor pressure and cell volume Diffusion barrier for macro-molecules and pathogens
Food reserves: endosperm cell walls degrade during seed during germination
CELLULOSE AND HEMICELLULOSE ARE PRESENT IN A MATRIX OF PECTIN POLYMERS
The plant cell wall is a laminate (薄板) of cellulose fibrils in a matrix of glycoprotein
Primary wall consists of the following basic features
– Cellulose (strength) – Hemicellulose
– Pectins (flexibility)
– Structural proteins (rigidity)
– Non-structural proteins
Cellulose micorfibrilsLiner chains of (1->4)-linked beta-D-glucose. Each microfibril may consists of6 to 30-50 chains. Each chain has 2000 to 25,000 glucose residues. Cellulose has a high tensile strength, equivalent to steel.
Insoluble, chemically stable. Excellent “bones”for building a strong cell wall.
a “glucan”: a polymer made up of glucose
…”xylan”……….…………..xylose Xyloglucan: a glucan backbone (a liner
chain of glucose) with xlylose attached as side chains
Cellulose molecules can be arranged together to form fibrils
that have great tensile strength.
These fibrils are the main structural element in the cell
walls of plants.
Loosening of the cell wall permits elongation of plant Auxin → induced weakening of cell wall → water into cell
→expansion of intracellular vaculoe →elongation of cell
Cell Wall Structure
The middle lamella, primarily pectin, ‘glues’ neighbouring cells together.
Primary cell wall:
The first wall laid down during growth.
This is soft and flexible so that the cell can expand during growth.
It contains a mixture of biopolymers, with typically ~20-30% cellulose
Once growth has stopped, the secondary cell wall is laid down, which provides structural support for the cells.
Secondary Cell Wall Structure:
Some cells have very thick secondary cell walls, to provide maximum support.
In the case of flax it can be μm in thickness (compared with ~100nm for the primary wall), and this was why flax was used for this study.
Typical cellulose content is ~50%, though can reach ~100% for e.g. cotton.
Structure is complex, and thought to consist of aligned 排成直線layers of cellulose microfibrils in a general biopolymer matrix, with systematic misorientations between the layers.
PLASMODESMATA INTERCONNECT CYTOPLASMS OF ADJACENT PLANT CELLS
60 nM diameter allows passage of molecules of up to 1000 MW
ER extensions (desmotubule) can pass through, allowing transit of membrane bound molecules
Elevation of cytosolic calcium inhibits transports (similar to gap junction)
The extracellular matrix and the cell wall are the “outside” of the cell Extracellular matrix (ECM): consists of collagen fibers and
proteoglycan. Collagen are a group of insoluble glycoproteins that
contain large amount of glycine and the hydroxylated forms of lysine and proline. (examples, tendons, cartilage, and bone)
Cell wall: consists cellulose microfibrils embedded in a matrix of other polysaccharides and small amounts of proteins (extensins)
Primary cell wall: cullulose fibrils and gel like polysaccharides, thus flexible and extensible
Secondary cell wall: additional cell wall materials deposited on the inner surface of the primary cell wall, thus thicker and rigid. Second cell wall also contains high concentration of lignin, a major component of Communication between cells:wood
Plasmadesmata: cytoplasmic bridges between plant cells
Animal cells: gap junctions, right junctions and adhesive junctions
Prokaryotes: cell walls consist of peptidoglycans with GlcNAc-MurNAc units