A theoretical model of Aquifex pyrophilus flagellin: implications for its thermostability

Abstract

Aquifex pyrophilus is a flagellated hyperthermophilic eubacterial species that grows optimally at 85 degrees C. The thermostable A. pyrophilus flagellar filament is primarily composed of a single protein called flagellin (FlaA). The N- and C-terminal sequence regions of FlaA are important for self-assembly and share high sequence similarity with mesophilic bacterial flagellins. We have developed a predictive 3D-structure of FlaA, using the published structure of mesophilic Salmonella typhimurium flagellin (FliC) as a template and analyzed it with respect to possible determinants of thermostability. A sequence comparison of FlaA and FliC revealed a +7.0% increase in FlaA hydrophobic residues, a +0.6% increase in charged residues and a corresponding decrease of -6.0% in polar residues. The FlaA N- and C-termini also have higher proportions of hydrophobic and charged residues at the expense of polar residues and higher non-polar surface areas. Thus, a predominant stabilizing factor in FlaA appears to be increased hydrophobicity, which often confers greater rigidity to proteins. Fewer intramolecular ion pairs were observed in FlaA than FliC, although an increase in the positive charge potential of the FlaA D0 and D1 domains was also observed; increased intermolecular salt bridges may also contribute to the thermal stability of the oligomeric flagellar fiber. [Figure: see text].

A Deletion Variant Study of the Functional Role of the Salmonella Flagellin Hypervariable Domain Region in Motility

“…It should be noted that thermostable flagellins from extremophilic Aquifex pyrophilus and Aquifex aeolicus eubacterial species have numbers of residues (∼500) similar to that of wild-type S. typhimurium phase 1 flagellin. [59][60][61] Thus, these thermostable flagellins have extensive hypervariable sequence regions that presumably form stabilizing globular outer domains. 59 It remains to be determined what structural mechanisms flagellins with smaller or absent hypervariable regions 21 use for stability and how they compare in motility relative to the S. typhimurium flagellin.…”

Structural predictions for curli amyloid fibril subunits CsgA and CsgB

“…Here, we utilize four freely available web servers, Robetta, 64,65 FALCON@home, 66,67 Quark 68 and RaptorX. 69,70 The Robetta ab initio method was used, which uses Rosetta's fragment insertion method, 71 which has been used successfully [72][73][74] and unsuccessfully 75 on a variety of proteins. While the Robetta server is well-established, it requires a signicant calculation time, which can be weeks to months for challenging models.…”

Flagellin gene (fliC) of Thermus thermophilus HB8: characterization of its product and involvement to flagella assembly and microbial motility

“…Our finding that T. thermophilus is able to possess flagella filaments arise new perspectives in research, since thermostable flagellins may have interesting applications in biotechnology and in nanotechnology (Malapaka and Tripp 2006). Flagellin filaments from T. thermophilus could be excellent candidates for the development of novel hybrid nanostructures, or nanotubes.…”

“…This filament has an outer diameter of 12-25 nm, a 2-3-nm-diameter inner channel and can be 1-15 nm or more in length (Malapaka and Tripp 2006). The flagellar basal structure is engaged in protein secretion, before serving as the flagellar motor (Komoriya et al 1999).…”

“…A. Pantazaki : from self-assembly and protected from proteolytic degradation by binding of the FliS chaperon protein (Ozin et al 2003;Auvray et al 2001). The primary (phase 1) flagellin gene in Salmonella typhimurium is referred to as fliC, a secondary (phase 2) flagellin gene is named fljB, while other bacterial flagellin genes are flaA, hag and flaF (Malapaka and Tripp 2006). Depending on the bacterial species, flagellins have molecular masses ranging from 28 to 80 kDa (Winstanley and Morgan 1997).…”