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Virus crystallization is the transformation of viral components arranged into solid crystal particles. The crystals are composed of thousands of inactive forms of a particular virus arranged in the shape of a prism. The inactive nature of virus crystals provide advantages for immunologists to effectively analyze the structure and function behind viruses. Understanding of viral characteristics have been deepened in science thanks to the enhancement and diversity in crystallization technologies. Virus crystals are widely accepted in epidemiology as a method to understand viral patterns and mitigate potential disease outbreaks.

Historical background
Pre-20th century

Virus crystals originate back to the late 19th century where the first protein crystallization discoveries were made by German biologists Ritthausen and Osborne, mainly for hemoglobin in worms and fishes. These early observations were primarily regarded as laboratory curiosities. The development of techniques for protein crystallization was driven by the need to purify and demonstrate the purity of naturally occurring proteins. These discoveries on protein crystallization techniques ultimately led to its application in virology once scientists have discovered Tobacco Mosaic Viruses (TMV), which were the first ever viruses to be discovered.

1930s

Accurate visualization of viruses using microscopy was difficult as they are extremely small, with the smallest of viruses being about 20nm in diameter. Microscopy was therefore a relatively challenging field, and alternative methods of observation were needed for micro particles such as viruses. Wendell Stanley successfully crystallized TMV viruses and demonstrated that it retained its infectivity even in crystal form. It was during this time when researchers discovered that crystalized viruses could diffract X-rays, implying a complex structural mechanism in viral bodies. This breakthrough laid the foundation for further investigations into virus crystallography.

1950s, 1960s

Technological advancements in X-ray crystallography allowed scientists to determine the three-dimensional structures of viruses with greater accuracy. Significant contributions were made in this field by Dorothy Hodgkin, who determined the crystal structure of TMV using X-ray diffraction techniques. Watson and Crick, the discoverers of DNA structure and function, discovered that certain viruses such as TMV exhibit a specific geometric shape known as an icosahedron . Throughout the following decades, researchers continued to refine the methods of virus crystallography, leading to the determination of numerous virus structures, including the poliovirus, rhinovirus, and HIV. These advancements provided valuable insights into the mechanisms of viral infection and replication, facilitating the development of antiviral drugs and vaccines.

1990s-Today

Viruses surrounded with thick lipid membranes, however, were unable to form ordered crystals to obtain good X-ray diffraction . During the early 1990s, cryo-electron microscopy (cryo-EM) had emerged as a powerful technique for studying virus structures. Cryo-EM allows scientists to visualize viruses at near-atomic resolution without the need for crystallization . Combination of both X-ray crystallography and electron microscopy gave information of virus anatomy, their response to antibodies and their role in fusion with the host cell. This has revolutionized the virology field, enabling determination of complex virus structures that were previously inaccessible.