Napsin-A is an
aspartic proteinase
Aspartic proteases are a catalytic type of protease enzymes that use an activated water molecule bound to one or more aspartate residues for catalysis of their peptide substrates. In general, they have two highly conserved aspartates in the active ...
that is encoded in humans by the NAPSA
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
.
The name napsin comes from ''n''ovel ''a''spartic ''p''roteinase of the
pep''sin'' family.
The activation peptide of an aspartic proteinase acts as an inhibitor of the active site. These peptide segments, or pro-parts, are deemed important for correct folding, targeting, and control of the activation of aspartic proteinase
zymogen
In biochemistry, a zymogen (), also called a proenzyme (), is an inactive precursor of an enzyme. A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the activ ...
s. The pronapsin A gene is expressed predominantly in lung and kidney. Its
translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
product is predicted to be a fully functional,
glycosylated
Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not ...
aspartic proteinase precursor containing an
RGD motif
Arginylglycylaspartic acid (RGD) is the most common peptide motif responsible for cell adhesion to the extracellular matrix (ECM), found in species ranging from ''Drosophila'' to humans. Cell adhesion proteins called integrins recognize and bind ...
and an additional 18 residues at its
C-terminus.
Utility
Detection of NAPSA gene expression can be used to distinguish
adenocarcinomas from other forms of
lung cancer
Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. Lung carcinomas derive from transformed, malign ...
.
References
Further reading
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{{gene-19-stub
Human proteins