Probing heavy metal binding to phycobiliproteins

Abstract

Blue‐green algae, also known as cyanobacteria, contain some of the most efficient light‐harvesting complexes known. These large, colourful complexes consist of phycobiliproteins which are extremely valuable in the cosmetics, food, nutraceutical and pharmaceutical industries. Additionally, the colourful and fluorescent properties of phycobiliproteins can be modulated by metal ions, making them highly attractive as heavy metal sensors and heavy metal scavengers. Although the overall quenching ability metal ions have on phycobiliproteins is known, the mechanism of heavy metal binding to phycobiliproteins is not fully understood, limiting their widespread quantitative applications. Here, we show using high‐resolution native mass spectrometry that phycobiliprotein complexes bind metal ions in different manners. Through monitoring the binding equilibria and metal‐binding stoichiometry, we show in particular copper and silver to have drastic, yet different effects on phycobiliprotein structure, both copper and silver modulate the overall complex properties. Together, the data reveals the mechanisms by which metal ions can modulate phycobiliprotein properties which can be used as a basis for the future design of metal‐related phycobiliprotein applications.

Assessment of Metal Accumulation by Arthrospira platensis and Its Adaptation to Iterative Action of Nickel Mono- and Polymetallic Synthetic Effluents

“…It is known that both phycocyanin and allophycocyanin bind heavy metal ions differentially, whereas phycocyanin has a higher affinity for them. Thus, metal binding preferentially to phycocyanin can be one of the reasons explaining the significant decrease in their content [ 34 ]. The same authors reported that silver and copper ions show minimal binding to allophycocyanin, as they induce structural changes such as a decrease in absorbance and fluorescence of phycocyanin.…”

“…In our previous study, we showed that in spirulina biomass grown in a Cr/Fe system, the content of phycobiliproteins was reduced by approximately 70% [ 18 ]. Since Bellamy-Carter and co-authors [ 34 ] reported little to no binding of iron ions by phycobilins, it can be suggested that nickel and chromium are responsible for the decrease of phycobiliproteins.…”

The increasing role of structural proteomics in cyanobacteria

“… The figure showcases how structural MS can provide information on oligomeric states and complex topology [ 56 , 57 ], protein–ligand or protein–metal interactions [ 58 ] and protein conformations [ 59 ] through native MS. PTMs can be determined through intact mass [ 60 ] combined with bottom-up and top-down approaches [ 61 ] with cross-linking MS [ 62 ] and protein footprinting [ 63 ] revealing information about transient interactions and protein binding interfaces. …”

Determination of Heavy Metal Content: Arsenic, Cadmium, Mercury, and Lead in Cyano-Phycocyanin Isolated from the Cyanobacterial Biomass

“…The α-subunit of C-PC contains a phycocyanobilin covalently attached to α-84 cysteine, while the β-subunit contains two phycocyanobilins that are linked to the β-84 and β-155 cysteine residues of the apoprotein, respectively [26]. The mechanisms underlying heavy metal binding to C-phycocyanin may vary with the different metal cations, but they are not fully understood [12]. Gelagutashvili E. and others distinguished two feasible ways of heavy metal ion binding to C-PC: site-specific and non-specific (diffuse) binding.…”

“…Therefore, there is a valid concern about the binding of heavy metals to C-PC. The level of C-PC contamination with metal ions depends on various factors, including the geographical location of the water body, the concentrations of heavy metals, the algae content in the water body, the water temperature, the pH, and the methods used for isolation and purification [6,[10][11][12]. Consequently, the need for necessary monitoring and evaluation of heavy metals in C-PC using the latest research methods is crucial to ensure the safety aspects related to the content of heavy metals in raw materials of natural origin and to maintain their quality.…”