The new diagnostic tests is based on our knowledge of the many mutations that are commonly found in fluconazole resistance in Candida. In order to change the fluconazole target protein to a resistant form there must be a mutation in the DNA encoding the gene. This mutation will change the genetic code and the new protein will be slightly different to the normal fluconazole sensitive one.

Over the years many researchers have studied such fluconazole resitance mutations. To simplify this tutorial we will focus on only one such type of mutation but many exist and there are likely to be others that have not been found yet. It is also possible that mutations in other genes can result in fluconazole resistance - hence the importance of doing the classical resistance test. (see reviews)

The mycologists explain...

here is the protein sequence of the C. albicans Sterol 14 demethylase gene that is targeted by fluconazole:

MAIVETVIDGINYFLSLSVTQQISILLGVPFVYNLVWQYLYSLRKDRAPLVFYWIPWFGSAASYGQQPYE 71
FFESCRQKYGDVFSFMLLGKIMTVYLGPKGHEFVFNAKLSDVSAEDAYKHLTTPVFGKGVIYDCPNSRLM 141
EQKKFAKFALTTDSFKRYVPKIREEILNYFVTDESFKLKEKTHGVANVMKTQPEITIFTASRSLFGDEMR 211
RIFDRSFAQLYSDLDKGFTPINFVFPNLPLPHYWRRDAAQKKISATYMKEIKSRRERGDIDPNRDLIDSL 281
LIHSTYKDGVKMTDQEIANLLIGILMGGQHTSASTSAWFLLHLGEKPHLQDVIYQEVVELLKEKGGDLND 351
LTYEDLQKLPSVNNTIKETLRMHMPLHSIFRKVTNPLRIPETNYIVPKGHYVLVSPGYAHTSERYFDNPE 421
DFDPTRWDTAAAKANSVSFNSSDEVDYGFGKVSKGVSSPYLPFGGGRHRCIGEQFAYVQLGTILTTFVYN 491
LRWTIDGYKVPDPDYSSMVVLPTEPAEIIWEKRETCMF

and here is a fluconazole resistant protein - the mutation is in red:

MAIVETVIDGINYFLSLSVTQQISILLGVPFVYNLVWQYLYSLRKDRAPLVFYWIPWFGSAASYGQQPYE 71
FFESCRQKYGDVFSFMLLGKIMTVYLGPKGHEFVFNAKLSDVSAEDAYKHLTTPVFGKGVIYDCPNSRLM 141
EQKKFAKFALTTDSFKRYVPKIREEILNYFVTDESFKLKEKTHGVANVMKTQPEITIFTASRSLFGDEMR 211
RIFDRSFAQLYSDLDKGFTPINFVFPNLPLPHYWRRDAAQKKISATYMKEIKSRRERGDIDPNRDLIDSL 281
LIHSTYKDGVKMTDQEIANLLIGILMGGQHTSASTSAWFLLHLGEKPHLQDVIYQEVVELLKEKGGDLND 351
LTYEDLQKLPSVNNTIKETLRMHMPLHSIFRKVTNPLRIPETNYIVPKGHYVLVSPGYAHTSERYFDNPE 421
DFDPTRWDTAAAKANSVSFNSSDEVDYGFGKVSKGVSSPYLPFGGGKHRCIGEQFAYVQLGTILTTFVYN 491
LRWTIDGYKVPDPDYSSMVVLPTEPAEIIWEKRETCMF

so if there is a change in the protein there must be a change in the gene encoding the protein?

- right - no problem, bring on the DNA

- yeah, right, whatever

- erm - no?

- help! Tell me about coding sequences and transcription and translation RIGHT NOW