Grade 11 Functions Textbook Nelson Pdf 31: Learn the Essential Skills and Concepts for University

Like mammalian precursor molecules (Steiner, 1998), the initial cleavages in C. elegans occur C-terminal to dibasic residues flanking the peptide sequence (Rosoff et al., 1993; Marks et al., 1995, 1997, 1998, 1999a, 2001; Husson et al., 2005, 2006); however, cleavages C-terminal to mono- and tribasic residues have also been reported (Rosoff et al., 1993; Marks et al., 1997, 2001). The enzymes responsible for the initial endoproteolytic cleavage are kex2/subtilisin-like proprotein convertases, which must themselves be cleaved to become active. Cleavage of proprotein convertase is dependent on a chaperonin protein SBT-1 7B2 (Lindberg et al., 1998; Sieburth et al., 2005). Four C. elegans proprotein convertases, kpc-1, egl-3/kpc-2, aex-5/kpc-3, and bli-4/kpc-4, are present in C. elegans (Thacker and Rose, 2000). egl-3/kpc-2 is expressed in many, but not all neurons in the nervous system (Kass et al., 2001). Loss of egl-3/kpc-2 results in defects in egg-laying, mechanosensation, and locomotion (Kass et al., 2001; Jacob and Kaplan, 2003), indicating that EGL-3/KPC-2 cleaves precursors whose peptides have diverse functions. Moreover, using a polyclonal anti-FMRFamide antibody that recognizes the Arg-Phe-amide but not the non-amidated Arg-Phe-OH moiety (Marder et al., 1987), Kass and co-workers (2001) found decreased FMRFamide-like immunoreactivity in egl-3/kpc-2 mutants, suggesting that egl-3/kpc-2 cleaves some, but not all FLP precursors and that other proprotein convertases are active in the same cells. Among the other proprotein convertases, a kpc-1 deletion mutant shows mild locomotory defects and slow growth, suggesting that KPC-1 cleaves precursors of peptides involved in movement and growth (Thacker and Rose, 2000). Mutations in aex-5/kpc-3 cause defecation defects (Thomas, 1990). aex-5/kpc-3 is expressed in muscle (Thacker and Rose, 2000), and has been proposed to cleave a precursor molecule in muscle to produce a peptide that serves as a retrograde signal to regulate exocytosis (Doi and Iwasaki, 2002). A major function of BLI-4/KPC-4 is to cleave procollagen into collagen so that it can be deposited in the cuticle to give the cuticle structural integrity. Hence, null alleles of bli-4/kpc-4 cause lethality (Thacker et al., 1995). However, transcripts of bli-4/kpc-4 are also expressed in the nervous system (Thacker et al., 1995; Thacker and Rose, 2000), although phenotypes associated with loss of bli-4/kpc-4 neural transcripts are unknown. Collectively, these data indicate that multiple proprotein convertases are active in neurons.

Grade 11 Functions Textbook Nelson Pdf 31

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