Abstract
The lacY from Escherichia coli strains 020 and AE43 have been cloned on plasmids which were designated p020-K358T and pAE43-D237N. These lacY mutants contain amino acid substitutions changing Lys-358 to Thr or Asp-237 to Asn, respectively. The charge neutralizing effect of each mutation is associated with a functional defect in melibiose transport which we exploited in order to isolate second site revertants to th melibiose-positive phenotype. Eleven melibiose-positive revertants of p020-K358T were isolated. All contained a second-site mutation converting Asp-237 to a neutral amino acid (8 to Asn, 1 to Gly, and 2 to Tyr). Twelve melibiose-positive revertants of pAE43-D237N were isolated. Two were second-site revertants converting Lys-358 to a neutrally Gln residue, while the remainder directly reverted Asn-237 to the wild-type Asp-237. We conclude that the functional intimate relationship between Asp-237 and Lys-358 suggests that these residues may be closely juxtaposed in three-dimensional space, possibly forming a 'charge-neutralizing' salt bridge.
Original language | English (US) |
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Pages (from-to) | 177-186 |
Number of pages | 10 |
Journal | BBA - Biomembranes |
Volume | 1062 |
Issue number | 2 |
DOIs | |
State | Published - Feb 25 1991 |
Externally published | Yes |
Keywords
- Aspartic acid 237
- Cotransport
- Lactose carrier
- Lysine 358
- Membrane transport
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Cell Biology