Phosphatidylinositol 3-Kinase Class III
Classes of Phosphatidylinositol 3-Kinase
Proteins are tantamount for life. The regulations of organism’s biological activities are entirely dependent on 22 deceivingly simple amino acids. However when linked into a linear chain they establish primary, secondary, tertiary and quaternary structures that host an almost limitless range of biological functions.
The variation between amino acid R-group (or side chain) ultimately decides the fate of protein structure as van der Waal momentary dipoles, ionic interaction between charged groups, attractions between polar groups and covalent bonds generate atomic and molecular interactions between constituting amino acids and protein subunits.
Thereby differing amino acid sequences culminate to dissimilar structures and fundamental functions giving proteins varying classes. Here the PI3K family is divided into three classes. Their classification can be based on the aforementioned structural variation that exists between proteins but also their regulative function and in vitro lipid substrate specificity.
Class I
PI3K class I is heterodimeric protein. Heterodimeric means PI3K is composed of two different molecules or subunits. One of the subunits functions is in regulation (p85) and the other is catalysis (p110). There are five versions of the p85 regulatory subunit and three versions of the p110 catalytic subunit. They can be seen in the table below.
Class II
PI3K class II is differentiated by structure and function. Functionally class II are only involved in catalysis with no regulatory subunits. The defining functional characteristic is they are Ca2+ independent for binding in vitro lipid substrates.Structurally class II has a C-terminal C2 domain in all three isoforms.
Class III
PI3K class III is almost analogous with class I structurally as it is heterodimeric. However functionally it contributes mainly to the transportation of proteins and vesicles.
Figure 1. Classes of Phophatidylinositol 3-Kinase and their associated genes.