Stabilization of Human Serum Albumin by the Binding of Phycocyanobilin, a Bioactive Chromophore of Blue-Green Alga Spirulina: Molecular Dynamics and Experimental Study

Abstract

Phycocyanobilin (PCB) binds with high affinity (2.2 x 106 M-1 at 25°C) to human serum albumin (HSA) at sites located in IB and IIA subdomains. The aim of this study was to examine effects of PCB binding on protein conformation and stability. Using 300 ns molecular dynamics (MD) simulations, UV-VIS spectrophotometry, CD, FT-IR, spectrofluorimetry, thermal denaturation and susceptibility to trypsin digestion, we studied the effects of PCB binding on the stability and rigidity of HSA, as well as the conformational changes in PCB itself upon binding to the protein. MD simulation results demonstrated that HSA with PCB bound at any of the two sites showed greater rigidity and lower overall and individual domain flexibility compared to free HSA. Experimental data demonstrated an increase in the α-helical content of the protein and thermal and proteolytic stability upon ligand binding. PCB bound to HSA undergoes a conformational change to a more elongated conformation in the binding pockets of HSA. PCB binding to HSA stabilizes the structure of this flexible transport protein, making it more thermostable and resistant to proteolysis. The results from this work explain at molecular level, conformational changes and stabilization of HSA structure upon ligand binding. The resultant increased thermal and proteolytic stability of HSA may provide greater longevity to HSA in plasma.

Characterisation and the effects of bilirubin binding to human fibrinogen

“…Phycocyanobilin, a molecule with the structure similar to bilirubin, binds to and stabilises human serum albumin (HSA) by increasing its α-helical content and the melting point [22].…”

Spirulina Phycobiliproteins as Food Components and Complements

“…There is no literature data related to transport of PC-derived peptides or PCB from gastrointestinal tract to circulation. Our previous studies demonstrated that PCB binds to human serum albumin (HSA) with high affinity (2.2 × 10 6 M −1 ) [37], and stabilizes protein structure [38], suggesting that in circulation HSA most likely transports PCB to tissues, similar to other bioactive food-derived substances. Many studies observed in vitro effects of C-PC in cell culture, but the location of protein inside cells is controversial and it is still unknown whether C-PC requires a transport protein carrier to enter cells.…”

Functionalized Alpha‐lactalbumin Conjugated with Gold Nanoparticle for Targeted Drug Delivery

“…On the other hand, the author reported that α‐helix content of HSA (50.4 %) was increased substantially to 55.2 % when in complexation with phycocyanobilin molecule confirmed by CD data. They suggested that phycocyanobilin binding with HSA provides stabilization, which was reflected in increase of helicity and decrease in random coil percentage from m 8.8 % to 4.8 % . The computational study showed that amino acid residues in α‐helices have exceptionally more non‐covalent interactions than residues in β‐strands .…”

“…They suggested that phycocyanobilin binding with HSA provides stabilization, which was reflected in increase of helicity and decrease in random coil percentage from m 8.8 % to 4.8 % . The computational study showed that amino acid residues in α‐helices have exceptionally more non‐covalent interactions than residues in β‐strands . In agreement with this, our findings suggest that the formation of ALA‐drug conjugates provides energy stabilization, which allows more weak interactions that can accommodate drug molecules on protein active site by helix conformation.…”