Retroviral aspartyl proteases are single domain aspartyl proteases from retroviruses, retrotransposon

Retrotransposon

Retrotransposons are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms. They are a subclass of transposon. They are particularly abundant in plants, where they are often a principal component of nuclear DNA...

s, and badnaviruses (plant dsDNA viruses). These proteases are generally part of a larger pol or gag polyprotein. Retroviral proteases are homologous to a single domain of the two-domain eukaryotic aspartyl proteases such as pepsin

Pepsin

Pepsin is an enzyme whose precursor form is released by the chief cells in the stomach and that degrades food proteins into peptides. It was discovered in 1836 by Theodor Schwann who also coined its name from the Greek word pepsis, meaning digestion...

s, cathepsin

Cathepsin

Cathepsins are proteases: proteins that break apart other proteins, found in many types of cells including those in all animals. There are approximately a dozen members of this family, which are distinguished by their structure, catalytic mechanism, and which proteins they cleave...

s, and renin

Renin

Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...

s .

Aspartic endopeptidases of vertebrate, fungal and retroviral origin have been characterised. More recently, aspartic endopeptidases associated with the processing of bacterial type 4 prepilin and archaean preflagellin have been described.

Structurally, aspartic endopeptidases are bilobal enzymes, each lobe contributing a catalytic Asp residue, with an extended active site cleft localized between the two lobes of the molecule. One lobe has probably evolved from the other through a gene duplication event in the distant past. In modern-day enzymes, although the three-dimensional structures are very similar, the amino acid sequences are more divergent, except for the catalytic site motif, which is very conserved. The presence and position of disulphide bridges are other conserved features of aspartic peptidases. All or most aspartate peptidases are endopeptidases. These enzymes have been assigned into clans (proteins which are evolutionary related), and further sub-divided into families, largely on the basis of their tertiary structure.

Retroviral aspartyl protease is synthesised as part of the POL polyprotein that contains; an aspartyl protease, a reverse transcriptase

Reverse transcriptase

In the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...

, RNase H

RNase H

The enzyme RNase H is a non-specific endonuclease and catalyzes the cleavage of RNA via a hydrolytic mechanism. Members of the RNase H family can be found in nearly all organisms, from archaea to bacteria and eukaryota....

 and integrase

Integrase

Retroviral integrase is an enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell...

. POL polyprotein undergoes specific enzymatic cleavage to yield the mature proteins.