Bioinformatics analysis of haptoglobin protein: an approach towards colon cancer biomarkers identification / Nur Nadia Suraya Suddin

Haptoglobin (Hp) is a hemoglobin-binding plasma protein consisting of two types of chains, called alpha (a) and beta (β), which originate from a common polypeptide. In humans, but not in other mammals, Hp has been shown to occur in two allelic forms, Hp 1 and Hp2, which differ in the length of the a-chain. The longer a-chain (in Hp2) seems to have arisen by an internal duplication of a gene segment coding for almost the entire a-chain of Hp 1.β chains of hp is more heavier than its a chains. The a-chain contains a complement control protein (CCP) domain and the b-chain contains a serine proteinase (SP) related domain. Hp plays a major role in binding to hemoglobin (Hb) and thereby inhibits its oxidative activity .It also acts as immunomodulatory and chaperone-like properties. It was reported that the Hp protein level increased during carcinogenesis and has been revealed to support angiogenesis. In this study, the identification of haptoglobin protein as a colon cancer biomarker was reported using bioinformatics analysis prediction approaches. Hp protein consist of 340 amino acids with the predicted value of both Mw and pl are 38415. 7 Da and 6.26 respectively. Hp protein is a hydrophilic protein due to its GRAVY value shows the negative value, -0.312. It is considered stable in nature. Its aliphatic index is 83.98. From the analyzed data, this protein consists of 35% of a­ helix, 28% of β-sheet, 24.5% of β-tums and 17.2% of coils loops. Hp protein is mainly found in an extracellular cell compared to intracellular. There are two domains found in the hp protein which are Sushi and Trypsin_ Dom. Sushi domains are known to be involved in many recognition processes, including the binding of several complement factors to fragments C3b and C4b whereas Trypsin_Dom (trypsin family which is known as serine protease) usually involves in catalytic activity .From the multiple sequence alignment, it illustrated that human,orang utan, rabbit ,mouse, cattle and monkey share high sequence similarity. However, according to the phylogenetic tree, orang utan haptoglobin is the most similar towards human haptoglobin. As a conclusion, the information obtained from bioinformatics analysis of haptoglobin protein would then provide preliminary information for identification biomarker for colon cancer study.