Hans Charles Freeman

21: Elegance in Molecular Design: The Copper Site of Photosynthetic Electron-Transfer Protein (1978)

Introduction

21: elegance in molecular design: the copper site of photosynthetic electron-transfer protein (1978). Discover the elegant molecular design of plastocyanin's copper site, crucial for photosynthetic electron transfer. Insights into its unique properties and function.

Abstract

The Liversidge Research Lecture, delivered before the Royal Society of New South Wales, 19th July, 1978. Reproduced by permission of the Royal Society of New South Wales from J. Proc. Roy. Soc. N.S.W., 1979, 112, 45-62."Plastocyanin is an intensely blue protein which is essential for photosynthesis in green leaves and in some algae. The blue colour is associated with the presence of a single copper atom in each molecule of the protein. In terms of the absorbance per copper atom, plastocyanin is about a hundred times as blue as 'normal' cupric compounds. In addition, the protein has an unusual electron spin resonance spectrum and an anomalously high redox potential. The combination of these properties occurs in some other copper-proteins but has not yet been mimicked in any model compound of low molecular weight.""The recent X-ray crystal structure analysis of plastocyanin has revealed a molecule ideally suited to the biological function which it performs. The nature of the copper site is such as to produce the high redox potential which is required for electron-transfer between plastocyanin and its neighbours in the photosynthetic chain. The location of the copper site in the protein molecule provides at least two reasonable electron-transfer pathways. The exterior of the molecule has distinctive features which suggest that the protein interacts in specific ways with its redox partners and/or its environment."

Review

This paper, based on the 1978 Liversidge Research Lecture, presents a compelling exploration into the elegance of molecular design within the photosynthetic electron-transfer protein, plastocyanin. The abstract immediately establishes the protein's critical role in photosynthesis and highlights its remarkable and then-unmimicked properties: an intense blue color, an unusual electron spin resonance spectrum, and an anomalously high redox potential, all associated with a single copper atom. The core contribution of this work, pivotal for its time, rests on the recent X-ray crystal structure analysis of plastocyanin, which elucidated how the molecule is ideally structured to perform its essential biological function. This structural insight provides a foundational understanding of how nature achieves such sophisticated biochemical capabilities. The review delves into the specifics of the copper site, revealing how its unique chemical environment is precisely tailored to generate the high redox potential required for efficient electron transfer between plastocyanin and its partners within the photosynthetic chain. Beyond the copper site itself, the abstract discusses the strategic location of this site within the protein, offering at least two plausible pathways for electron transfer, a crucial aspect for understanding reaction kinetics and efficiency. Furthermore, the exterior of the plastocyanin molecule is noted for its distinctive features, strongly suggesting specific interaction mechanisms with its redox partners and surrounding cellular environment. These structural details beautifully underscore the "elegance in molecular design" referenced in the title, demonstrating a high degree of evolutionary optimization for its specific biological role. This research, presented in 1978/79, represents a significant step forward in understanding the intricate structure-function relationships of metalloproteins. By providing the first detailed structural insights into plastocyanin's copper site, it not only explained previously observed anomalous properties but also opened new avenues for investigation into photosynthetic electron transfer mechanisms. The challenge posed by the abstract—to mimic these unique copper properties in low molecular weight compounds—would inspire decades of inorganic chemistry research. Ultimately, this work laid crucial groundwork for future studies in protein engineering, bioinorganic chemistry, and our broader comprehension of how biological systems harness metal ions for life-sustaining processes.

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