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CAPSID ASSEMBLY. "Bacteriophage P22 provides a well-studied example for assembly of capsids formed from subunits with the HK97-fold. Assembly of bacteriophage P22 in vivo proceeds via a nucleation-limited reaction in which 415 copies of coat protein (gp5, the product of gene 5) co-polymerize with 60–300 scaffolding proteins (gp8), the dodecameric portal protein complex (gp1), and ejection proteins (gp7, gp16 and gp20)." http://www.sciencedirect.com/science/article/pii/S0042682215001920 View in LinkedIn

DRAMATIC CAPACITY. "The versatility of the HK97-fold is also evident when comparing the diameters of capsids with confirmed HK97-like coat proteins, which range from ~24 nm to ~185 nm. This fold evolved to accommodate these dramatic differences in capsid diameter and the varying degrees of capsid curvature accompanying the spectrum of diameters." http://www.sciencedirect.com/science/article/pii/S0042682215001920 View in LinkedIn

PENTON AND HEXON SUBUNITS. "In capsids, HK97-like coat protein subunits are organized into pentons and hexons. An exception would be for capsids with a triangulation (T) number of 1, which would be composed entirely of pentons." http://www.sciencedirect.com/science/article/pii/S0042682215001920 View in LinkedIn

OTHER COMMON STRUCTURES. "Viruses using the HK97-fold share unexpected similarities beyond the fold of their coat proteins including the architecture of their virions, an internal scaffolding (or Δ-domain) protein-mediated assembly, active dsDNA packaging, and capsid maturation events." (dsDNA = double stranded DNA). http://www.sciencedirect.com/science/article/pii/S0042682215001920 View in LinkedIn

EMBELLISHMENTS ADD FUNCTIONALITY. "In addition to varied sizes, an amazing diversity of loop and domain embellishments to the basic HK97-fold increase its functionality and often provide alternate ways to stabilize the assembled particles. Particles containing subunits with the HK97-fold will undoubtedly continue to be discovered with other variations for accomplishing folding, assembly, and capsid stabilization." http://www.sciencedirect.com/science/article/pii/S0042682215001920 View in LinkedIn

Missing reference: https://lnkd.in/dXvJFtt View in LinkedIn

SIZE AND FUNCTION OF CAPSID. "The capsid size has likely evolved to accommodate the size of the material to be packaged as T. maritima encapsulins package small ferritin-like proteins inside a particle with an inner volume of 4.18×10(6) Å3 while Phage G requires a much larger capsid (inner volume=1.87×10(9) Å3) to package its 670 kb chromosome." https://lnkd.in/dXvJFtt View in LinkedIn

STRUCTURE ACROSS KINGDOMS. "The majority of capsids using the HK97-fold are of viruses infecting bacteria (bacteriophage or phage). However, this fold is also found in the coat protein floor domain of eukaryotic Herpesvirdae, including Herpes simplex virus type 1 (HSV-1), murine cytomegalovirus (MCMV), pseudorabies virus (PRV), and rhesus monkey rhadinovirus (RRV), as well as the archaeal Haloarcula sinaiiensis tailed virus 1 (HSTV-1)." View in LinkedIn

BASIC TEMPLATE. "The HK97-fold, despite sequence, structural, and functional divergences, is a basic template for formation of a proteinacious shell utilized by viruses and prokaryotic cells alike. The protein shell, composed of HK97-like subunits, serves a protective role for the genomes of viruses infecting all three domains of life. Prokaryotic cells also utilize the HK97-fold to form encapsulin nanocompartments, and possibly gene transfer agent particles that contribute to high frequencies of horizontal gene transfer." http://www.sciencedirect.com/science/article/pii/S0042682215001920 View in LinkedIn

FRAGMENT FROM NATURE continues from last weekend on the most prevalent protein fold in nature. These structures are widely used as templates for constructions across kingdoms. When mutations of these folds occur in viruses, where they originated, they result in non-infective particles. That the most plentiful life form would produce the most plentiful and flexible structures, acquired by lateral gene transfer, is probably of little surprise. View in LinkedIn