Related Experiment Video

Updated: Aug 8, 2026

Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo
10:53

Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo

Published on: November 8, 2013

Identification of a keratin-associated protein that localizes to a membrane compartment

C F Chou1, C L Riopel, M B Omary

  • 1Palo Alto Veterans Administration Medical Center, CA 94304.

The Biochemical Journal
|March 1, 1994
PubMed

Insights

Researchers identified an 85 kDa acidic glycoprotein, Keratin-Associated Protein (KAP85), that binds to keratin intermediate filaments (K8/18) in simple epithelia, potentially linking them to the plasma membrane.

Area of Science:

  • Cell Biology
  • Biochemistry
  • Epithelial Biology

Background:

  • Keratin intermediate filaments (K8/18) are crucial structural components in simple epithelia.
  • The precise mechanisms of keratin filament association with cellular structures remain incompletely understood.

Purpose of the Study:

  • To characterize an acidic glycoprotein associated with keratin intermediate filaments.
  • To elucidate the role of this glycoprotein in keratin filament organization and cellular localization.

Main Methods:

  • Co-immunoprecipitation using anti-keratin monoclonal antibodies with K8/18 from HT29 cells.
  • In vitro galactosylation and NaIO4/NaB3H4 labeling to assess glycoprotein detection.
  • Glycosidase digestion to analyze oligosaccharide composition.
  • Cellular fractionation to determine protein localization.

Main Results:

  • An 85 kDa acidic glycoprotein, termed KAP85, was identified and co-immunoprecipitated with keratin 8 and 18 (K8/18).
  • KAP85 detection via galactosylation varied with cell cycle, suggesting changes in terminal N-acetylglucosamine residues.
  • KAP85 contains high mannose and complex oligosaccharides and exclusively associates with the cytoskeletal K8/18 pool.
  • Subcellular fractionation revealed KAP85 co-localization with a plasma-membrane-enriched fraction.

Conclusions:

  • KAP85 is a novel keratin-associated protein in simple epithelia.
  • This membrane-associated glycoprotein may function as an attachment site for keratin intermediate filaments (K8/18).
  • KAP85's interaction could be critical for keratin filament organization and linkage to the plasma membrane.

More Related Videos

Determining Membrane Protein Topology Using Fluorescence Protease Protection (FPP)08:14

Determining Membrane Protein Topology Using Fluorescence Protease Protection (FPP)

Published on: April 20, 2015

Determination of Plasma Membrane Partitioning for Peripherally-associated Proteins11:11

Determination of Plasma Membrane Partitioning for Peripherally-associated Proteins

Published on: June 15, 2018

Related Concept Videos

Membrane Domains01:18

Membrane Domains

The membrane domains concentrate specific lipids and proteins at one place within the membrane, which helps in cell signaling, adhesion, and other critical cellular processes. These domains can differ in size, composition, function, and lifespan.
Protein Domains
The membrane comprises a group of distinct proteins responsible for carrying out a cell's specific function. For example, the plasma membrane of the human sperm, or a single germ cell, contains a unique set of proteins in the anterior...
Cytoskeletal Linker Proteins - Plakins01:09

Cytoskeletal Linker Proteins - Plakins

Plakins are large proteins with binding domains for microtubules, microfilaments, intermediate filaments, and membrane-associated protein complexes at cell junctions. Plakin functions are evolutionarily conserved and are primarily involved in organizing the different components of the cytoskeleton by crosslinking them to each other and connecting them to the cell-matrix and cell adhesion complexes. They are also known to interact with signal transducers, serve as scaffolds for signaling...
ER Retrieval Pathway01:45

ER Retrieval Pathway

In the secretory pathway, vesicles transport proteins from one cellular compartment to another in forward transport to deliver the protein to its correct location. Occasionally, misfolded proteins and incorrect proteins escape their original compartments, and a retrieval pathway is used to return the escaped proteins to their original compartment.
The ER uses many checkpoints to prevent the entry of incorrectly folded or a resident protein as cargo onto a transport vesicle. These mechanisms...
Mechanisms of Membrane Domain Formation00:59

Mechanisms of Membrane Domain Formation

Different physical properties of lipids and proteins allow them to localize and form distinct islands or domains in the membrane. Some membrane domains are formed due to protein-protein interactions, whereas others are formed due to the presence of specific lipids such as sphingolipids and sterols—for example, large proteins, such as bacteriorhodopsin, aggregate and create distinct domains.
Another mechanism for membrane domain formation involves membrane proteins interacting with cytoskeletal...
Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the translocon complex.
Protein Transport to the Inner Chloroplast Membrane01:18

Protein Transport to the Inner Chloroplast Membrane

Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...