The Contributions of the Amino and Carboxy Terminal Domains of Flightin to the Biomechanical Properties of Drosophila Flight Muscle Thick Filaments

Nathan S Gasek; Lori R Nyland; Jim O Vigoreaux

doi:10.3390/biology5020016

The Contributions of the Amino and Carboxy Terminal Domains of Flightin to the Biomechanical Properties of Drosophila Flight Muscle Thick Filaments

Biology (Basel). 2016 Apr 27;5(2):16. doi: 10.3390/biology5020016.

Authors

Nathan S Gasek¹, Lori R Nyland^{2

3}, Jim O Vigoreaux^{4

5}

Affiliations

¹ Department of Biology, University of Vermont, Burlington, VT 05405, USA. ngasek@uvm.edu.
² Department of Biology, University of Vermont, Burlington, VT 05405, USA. lori.nyland@med.uvm.edu.
³ Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA. lori.nyland@med.uvm.edu.
⁴ Department of Biology, University of Vermont, Burlington, VT 05405, USA. jvigorea@uvm.edu.
⁵ Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA. jvigorea@uvm.edu.

Abstract

Flightin is a myosin binding protein present in Pancrustacea. In Drosophila, flightin is expressed in the indirect flight muscles (IFM), where it is required for the flexural rigidity, structural integrity, and length determination of thick filaments. Comparison of flightin sequences from multiple Drosophila species revealed a tripartite organization indicative of three functional domains subject to different evolutionary constraints. We use atomic force microscopy to investigate the functional roles of the N-terminal domain and the C-terminal domain that show different patterns of sequence conservation. Thick filaments containing a C-terminal domain truncated flightin (fln(ΔC44)) are significantly shorter (2.68 ± 0.06 μm; p < 0.005) than thick filaments containing a full length flightin (fln⁺; 3.21 ± 0.05 μm) and thick filaments containing an N-terminal domain truncated flightin (fln(ΔN62); 3.21 ± 0.06 μm). Persistence length was significantly reduced in fln(ΔN62) (418 ± 72 μm; p < 0.005) compared to fln⁺ (1386 ± 196μm) and fln(ΔC44)(1128 ± 193 μm). Statistical polymer chain analysis revealed that the C-terminal domain fulfills a secondary role in thick filament bending propensity. Our results indicate that the flightin amino and carboxy terminal domains make distinct contributions to thick filament biomechanics. We propose these distinct roles arise from the interplay between natural selection and sexual selection given IFM's dual role in flight and courtship behaviors.

Keywords: Drosophila melanogaster; atomic force microscopy; flightin; myosin; persistence length; thick filament.