Chemokine ligand 3-like 1, also known as CCL3L1, is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 which in humans is encoded by the CCL3L1 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.

Function

This gene is one of several chemokine

Chemokine

Chemokines are a family of small cytokines, or proteins secreted by cells. Their name is derived from their ability to induce directed chemotaxis in nearby responsive cells; they are chemotactic cytokines...

 genes clustered on the q-arm of chromosome 17. Chemokines are a family of secreted proteins involved in immunoregulatory and inflammatory

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

 processes. Specifically, chemokines attract lymphocytes to sites of infection or damage. This protein binds to several chemokine receptors including chemokine binding protein 2 (CCBP2

CCBP2

Chemokine-binding protein 2 is a protein that in humans is encoded by the CCBP2 gene.-Further reading:...

 or D6) and chemokine (C-C motif) receptor 5 (CCR5

CCR5

C-C chemokine receptor type 5, also known as CCR5, is a protein that in humans is encoded by the CCR5 gene. CCR5 is a member of the beta chemokine receptors family of integral membrane proteins...

).

CCR5 is a co-receptor for HIV

HIV

Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...

, and binding of CCL3L1 to CCR5 inhibits HIV entry. Furthermore, the binding causes the receptor to be taken inside the cell by endocytosis

Endocytosis

Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...

, to eventually be reprocessed and re-expressed.

Gene organization

The human genome reference assembly

Reference genome

A reference genome is a digital nucleic acid sequence database, assembled by scientists as a representative example of a species' genetic code. As they are often assembled from the sequencing of DNA from a number of donors, reference genomes do not accurately represent the genetic code of any...

 contains two full copies of the gene (CCL3L1 and CCL3L3) and an additional partial duplication, which is thought to result in a pseudogene

Pseudogene

Pseudogenes are dysfunctional relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell...

, designated CCL3L2. This record represents the more telomeric full-length gene.

Clinical significance

The copy number of this gene varies among individuals. This is hypothesized to be due to segmental duplication of the region containing CCL3. Most individuals have 1-6 copies in the diploid genome, although rare individuals have zero or more than six copies. With increased copy number, there is more CCL3L1 expressed, and so competition for the CCR5 binding site is increased. This leads to slower advancement of disease in HIV-infected individuals, giving those with greater copy number more resistance.

Further reading