Question

The C-terminal region of complement-derived C5a (C5a65-74) represents a) the biologically active region of \(\mathrm{C} 5 \mathrm{a}\) b) a post-translational signal sequence c) a site for phosphorylation by kinases d) a immunogenic site recognized by T lymphocytes

Short answer

Answer: The C-terminal region of complement-derived C5a (C5a65-74) is a key part of the biologically active region of C5a.

Step-by-step solution

Identify the region of interest

Complement-derived C5a protein has a region named C5a65-74, which is located at the C-terminal part of the protein. We need to focus on this region to determine its biological role.

Analyzing the different options

The question presents four options for the possible roles of the C5a65-74 region of C5a: a) the biologically active region of C5a b) a post-translational signal sequence c) a site for phosphorylation by kinases d) an immunogenic site recognized by \(T\) lymphocytes

Identify the correct answer

The C-terminal region of complement-derived C5a (C5a65-74) is a key part of the biologically active region of C5a. Its primary activity is mediating the inflammatory response by binding to the C5a receptor along with the N-terminal region of C5a. This binding leads to chemotaxis, histamine release, and increase in blood vessels' permeability. It does not involve any post-translational signal sequence, phosphorylation by kinases, nor is it recognized by \(T\) lymphocytes as an immunogenic site.

Conclusion

Considering the information reviewed, the correct answer to the question is: a) the biologically active region of C5a

Key concepts

C5a function

C5a is an essential component of the complement system, playing a vital role in the body's immune response. The main function of C5a is to act as a potent chemoattractant. This means it attracts cells involved in the immune response.

• It guides immune cells, such as neutrophils, to the site of infection or injury.
• This helps in the clearance of pathogens and damaged cells, promoting healing.
• Additionally, C5a influences other immune processes by promoting inflammation via cell signaling.

C5a forms as part of the complement activation cascade when C5 is cleaved into C5a and C5b. Understanding its function provides insight into its importance in both acute and chronic inflammation responses.

C5a receptor

The C5a receptor, often referred to as C5aR or CD88, is a specific protein found on the surface of certain cells.

• These cells include immune cells like macrophages, neutrophils, and mast cells.
• When C5a binds to its receptor, it triggers a series of cellular responses.

One of the primary roles of the C5a receptor is to mediate the effects of C5a. This binding facilitates various immune responses, such as: - Induction of chemokinesis and chemotaxis, which are movements of cells toward the chemical stimulus. - Release of histamines leading to an increase in vascular permeability. The C5a-C5aR interaction is crucial for inflammation and helps in rapid recruitment of immune cells to sites where they are most needed.

Inflammation response

Inflammation is a vital response of the immune system to injury or infection. C5a plays a significant role in intensifying this response by: - Attracting immune cells to the affected site, which helps curb pathogens and start the healing process. - Enhancing the release of pro-inflammatory mediators like histamines. C5a and its receptor combine to amplify the inflammatory response. This contributes to the classic signs of inflammation: - Redness - Heat - Swelling - Pain This response is essential for host defense, but if unchecked, it can lead to chronic inflammatory conditions. Understanding the balance between beneficial and harmful inflammation is key in medical studies.

T lymphocytes

T lymphocytes, also known as T cells, are a type of white blood cell that play a central role in cell-mediated immunity.

• They are part of the adaptive immune system, recognizing and remembering specific pathogens.
• Unlike B cells, T cells do not produce antibodies.
• Instead, they recognize antigens presented by other cells and help modulate the immune response.

C5a is not directly recognized by T lymphocytes. However, the inflammation processes initiated by C5a and other complement components make environments conducive for T cell activation and proliferation. Hence, while C5a doesn’t interact with T cells directly, it greatly influences their activity in the immune response.

Protein phosphorylation

Protein phosphorylation is a biochemical process that involves the addition of a phosphate group to a protein molecule, an essential mechanism in cell signaling.

• This process serves as a molecular switch to activate or deactivate enzymes and receptors.
• It is a common post-translational modification that regulates various cellular activities.

In the context of C5a, its activity is not related to phosphorylation by kinases. The C5a (C5a65-74) region is primarily involved in receptor binding to exert its effects. While phosphorylation is crucial in many protein interactions, C5a's role in complement activation and inflammation does not rely on this modification.