alpha-1-acid glycoprotein

thumb|363x363px|Structure of human alpha-1-acid glycoprotein (AGP1) rendered in ChimeraX using PDB ID: 3KQ0 thumb|339x339px|Structure of human alpha-1-acid glycoprotein (AGP2) rendered in ChimeraX using PDB ID: 3APU Orosomucoid (ORM) or alpha-1-acid glycoprotein (α1AGp, AGP or AAG) is an acute phase protein found in plasma. Orosomucoid was discovered over 70 years ago and belongs to the lipocalin protein family. There are two isoforms of AGP, referred to as AGP1 and AGP2. It is an alpha-globulin glycoprotein and is modulated by two polymorphic genes. It is synthesized primarily in hepatocytes and has a normal plasma concentration between 0.6 and 1.2 mg/mL (1–3% plasma protein). Recent research has shown that under certain physiological conditions, brain and adipose tissue can also synthesize this protein. Plasma levels of AGP are affected by pregnancy, burns, certain drugs, and certain diseases, particularly HIV. APG also plays an important role in inflammation and pharmacokinetics, acting as a major transport protein in the blood stream.

== Structure == Orosomucoid is a highly glycosylated protein having a molecular weight of 34–54 kDa, with nearly 45% of its mass in carbohydrate sidechains. The isoforms AGP1 and AGP2 are encoded by the ORM1 and ORM2 genes on chromosome 9, and differ by only 22 amino acids This results in a slightly smaller beta-barrel in AGP2. The structural differences between AGP 1 and 2 allow for Alpha 1-acid glycoprotein to bind to a wider variety of ligands, broadening AGP's functional range. These chains contribute significantly to molecular stability and interaction potential with other molecules, including significant drugs. During systemic inflammation AGP concentration increases and its glycosylation pattern changes, generating various glycoforms with distinct — sometimes even opposing — biological activities. One study shows that at least 5 different functions can be linked to changes in the heteroglycan side chains. These side chain can be bi-, tri-, or tetra antennary, which contribute to the strength of binding to the ligand. It has been proven that during acute inflammation there is an increase of AGP glycoforms with biantennary units, this is a type I glycosylation change. In chronic inflammatory conditions, AGP often exhibits a reduction in glycoforms containing biantennary heteroglycans, this is a type II glycosylation shift. Similar changes in glycosylation patterns have also been observed during pregnancy, estrogen therapy, and liver injury.