What is the Difference Between Integral Peripheral and Surface Proteins

The key difference between integral peripheral and surface proteins is that integral and surface proteins are permanently embedded within the plasma membrane while peripheral protein is temporally associated with the plasma membrane. 

The plasma membrane contains molecules other than phospholipids. These molecules can be either proteins or carbohydrates. The plasma membrane contains certain types of proteins that play a very important role in cell function. A membrane protein is a molecule that attaches to or associates with the cell membrane of a cell or an organelle. They can be categorized into several types based on their association with the membrane. Integral peripheral and surface proteins are membrane proteins that are very important for cell activity.

CONTENTS

1. Overview and Key Difference
2. What are Integral Proteins
3. What are Peripheral Proteins
4. What are Surface Proteins
5. Similarities – Integral Peripheral and Surface Proteins
6. Integral vs Peripheral vs Surface Proteins in Tabular Form
7. Summary

What are Integral Proteins?

Integral protein is a membrane protein that locks itself into the cell membrane permanently. Therefore, they are permanent components of biological membranes. Integral protein is mainly classified into two types as transmembrane proteins and integral monotopic proteins. Transmembrane membrane protein spans the entire plasma membrane. On the other hand, integral monotopic protein is permanently attached to the membrane from only one side. The three-dimensional structure of approximately 160 different integral proteins has been determined at atomic resolution by nuclear magnetic resonance up to now.

Studying these proteins is very difficult due to the difficulties in their extraction and crystallization. Furthermore, the structures of many of these integral proteins are readily available in protein data banks (PDB). The integral membrane protein performs many different functions. It can function as transporters, linkers, channels, receptors, enzymes, structural membrane domains, and cell adhesion proteins. Moreover, it also involves in accumulation and transduction of energy. Some examples are cell adhesion proteins, rhodopsin and glucose permease, etc.

What are Peripheral Proteins?

Peripheral protein is a membrane protein that temporally associates with the plasma membrane.  It normally attaches to integral membrane proteins to penetrate the peripheral regions of the lipid bilayer. For example, the regulatory protein subunits of ion channels and transmembrane receptors may be defined as peripheral proteins. These proteins attach to integral proteins or lipid bilayers through a combination of hydrophobic, electrostatic, and other noncovalent interactions.

Peripheral protein can be dissociated following the treatment with a polar reagent (solution with high pH or high salt concentration). They may be post-translationally modified with added fatty acid, diacylglycerol or prenyl chains. Further, the main functions of peripheral protein are cell support, communication, enzymes and molecular transfer such as electron transfer.

What are Surface Proteins?

Surface proteins are membrane proteins permanently embedded in or spanning the layer of cell membranes of more complex organisms. Most cell surface proteins contain a carbohydrates component. Surface protein is integral to the way in which a cell interacts with the environment around it.

Some surface proteins are exposed to the external side of the membrane and have attached carbohydrate groups to their outer surfaces. They are called glycoproteins. They have different functions such as structural components, lubricants, hormones, enzymes, transport molecules, receptors, antifreeze proteins, regulation of development, homeostasis, etc. Moreover, cell surface protein is very important in biomedical science as 66% of approved human drugs listed in the DrugBank database target a cell surface protein.

Similarities Between Integral Peripheral and Surface Proteins

• Integral peripheral and surface proteins are membrane proteins.
• They are all made up of amino acids.
• All of them are connected to the lipid bilayer of biological cells.
• They are very important in cell survival.

Difference Between Integral Peripheral and Surface Proteins

Integral and surface proteins are permanently embedded within the plasma membrane, while peripheral protein is temporally associated with the plasma membrane.  So, this is the key difference between integral peripheral and surface proteins.

The following infographic lists more differences between integral peripheral and surface proteins in tabular form.

Summary – Integral vs Peripheral vs Surface Proteins

Membrane proteins represent an important class of proteins involved in essential cellular and physiological processes. A membrane protein is a molecule attached to or associated with the cell membrane of a cell or an organelle. They can be categorized into several types based on their association with the membrane. Integral peripheral and surface proteins are very important membrane proteins. Integral and surface proteins are permanently embedded within the plasma membrane. In contrast, peripheral protein is temporally associated with the plasma membrane. Thus, this is the summary of what is the difference between integral peripheral and surface proteins.

Reference:

1. “Membrane Protein.” An Overview | ScienceDirect Topics.
2. “Surface Proteins.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “OSC Microbio 03 03 PlasmaMem” By CNX OpenStax –  (CC BY 4.0) via Commons Wikimedia