Effect of pH on the secondary structure and thermostability of beetle luciferases: structural origin of pH-insensitivity

Author(s)

Tomazini, Atilio ; Carvalho, Mariele ; Murakami, Mario T. T. ; Viviani, Vadim R.

• Document type: Journal article
• Source: PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES; v. N/A, p. 12-pg., 2023-01-21.

Abstract

Beetle luciferases were classified into three functional groups: (1) pH-sensitive yellow-green-emitting (fireflies) which change the bioluminescence color to red at acidic pH, high temperatures and presence of heavy metals; (2) the pH-insensitive green-yellow-emitting (click beetles, railroad worms and firefly isozymes) which are not affected by these factors, and (3) pH-insensitive red-emitting. Although the pH-sensing site in firefly luciferases was recently identified, it is unclear why some luciferases are pH-insensitive despite the presence of some conserved pH-sensing residues. Through circular dichroism, we compared the secondary structural changes and unfolding temperature of luciferases of representatives of these three groups: (1) pH-sensitive green-yellow-emitting Macrolampis sp2 (Mac) and Amydetes vivianii (Amy) firefly luciferases; (2) the pH-insensitive green-emitting Pyrearinus termitilluminans larval click beetle (Pte) and Aspisoma lineatum (Al2) larval firefly luciferases, and (3) the pH-insensitive red-emitting Phrixotrix hirtus railroadworm (PxRE) luciferase. The most blue-shifted luciferases, independently of pH sensitivity, are thermally more stable at different pHs than the red-shifted ones. The pH-sensitive luciferases undergo increases of alpha-helices and thermal stability above pH 6. The pH-insensitive Pte luciferase secondary structure remains stable between pH 6 and 8, whereas the Al2 luciferase displays an increase of the beta-sheet at pH 8. The PxRE luciferase also displays an increase of alpha-helices at pH 8. The results indicate that green-yellow emission in beetle luciferases can be attained by: (1) a structurally rigid scaffold which stabilizes a single closed active site conformation in the pH-insensitive luciferases, and (2) active site compaction above pH 7.0 in the more flexible pH-sensitive luciferases. (AU)

• FAPESP's process: 10/05426-8 - Arthropod bioluminescence: biological diversity in Brazilian biomes, biochemical origin, structural/functional evolution of luciferases, molecular differentiation of lanterns, biotechnological, environmental and educational applications
• Grantee: Vadim Viviani
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 18/02538-1 - Resolution of the three-dimensional structures of beetle luciferases and related enzymes by X-ray crystallography: relationship between structure, bioluminescence spectra and oxygenase activity
• Grantee: Atílio Tomazini Júnior
• Support Opportunities: Scholarships in Brazil - Post-Doctoral